diff --git a/BUILD b/BUILD
index f49f4c250c..ca11f42b19 100644
--- a/BUILD
+++ b/BUILD
@@ -104,6 +104,7 @@ cc_library(
     srcs = [
         "upb/alloc.c",
         "upb/arena.c",
+        "upb/array.c",
         "upb/decode.c",
         "upb/encode.c",
         "upb/internal/table.h",
@@ -115,9 +116,11 @@ cc_library(
     hdrs = [
         "upb/alloc.h",
         "upb/arena.h",
+        "upb/array.h",
         "upb/decode.h",
         "upb/encode.h",
         "upb/extension_registry.h",
+        "upb/message_value.h",
         "upb/msg.h",
         "upb/status.h",
         "upb/string_view.h",
@@ -128,6 +131,7 @@ cc_library(
     visibility = ["//visibility:public"],
     deps = [
         ":arena_internal",
+        ":array_internal",
         ":decode_internal",
         ":encode_internal",
         ":extension_registry",
@@ -220,6 +224,7 @@ cc_library(
     copts = UPB_DEFAULT_COPTS,
     visibility = ["//visibility:public"],
     deps = [
+        ":array_internal",
         ":collections",
         ":mini_table",
         ":mini_table_internal",
@@ -276,6 +281,7 @@ cc_library(
     copts = UPB_DEFAULT_COPTS,
     deps = [
         ":arena_internal",
+        ":array_internal",
         ":decode_internal",
         ":extension_registry",
         ":port",
@@ -292,10 +298,13 @@ cc_library(
 cc_library(
     name = "generated_code_support__only_for_generated_code_do_not_use__i_give_permission_to_break_me",
     hdrs = [
+        "upb/array.h",
         "upb/decode.h",
         "upb/decode_fast.h",
         "upb/encode.h",
         "upb/extension_registry.h",
+        "upb/internal/array.h",
+        "upb/message_value.h",
         "upb/msg.h",
         "upb/msg_internal.h",
         "upb/port_def.inc",
@@ -340,12 +349,10 @@ upb_proto_reflection_library(
 cc_library(
     name = "collections",
     srcs = [
-        "upb/array.c",
         "upb/map.c",
         "upb/msg_internal.h",
     ],
     hdrs = [
-        "upb/array.h",
         "upb/collections.h",
         "upb/map.h",
         "upb/message_value.h",
@@ -718,6 +725,27 @@ cc_library(
 
 # Internal C/C++ libraries #####################################################
 
+cc_library(
+    name = "array_internal",
+    srcs = [
+        "upb/alloc.h",
+        "upb/arena.h",
+        "upb/array.h",
+        "upb/internal/array.c",
+        "upb/message_value.h",
+        "upb/msg.h",
+        "upb/status.h",
+        "upb/string_view.h",
+        "upb/upb.h",
+    ],
+    hdrs = ["upb/internal/array.h"],
+    copts = UPB_DEFAULT_COPTS,
+    visibility = ["//:__subpackages__"],
+    deps = [
+        ":port",
+    ],
+)
+
 cc_library(
     name = "arena_internal",
     srcs = [
@@ -787,6 +815,7 @@ upb_amalgamation(
     ],
     libs = [
         ":arena_internal",
+        ":array_internal",
         ":collections",
         ":decode_internal",
         ":descriptor_upb_proto",
@@ -816,6 +845,7 @@ upb_amalgamation(
     ],
     libs = [
         ":arena_internal",
+        ":array_internal",
         ":collections",
         ":decode_internal",
         ":descriptor_upb_proto",
@@ -848,6 +878,7 @@ upb_amalgamation(
     ],
     libs = [
         ":arena_internal",
+        ":array_internal",
         ":collections",
         ":decode_internal",
         ":descriptor_upb_proto",
diff --git a/upb/arena.c b/upb/arena.c
index 85eaf78c02..15e7a6b180 100644
--- a/upb/arena.c
+++ b/upb/arena.c
@@ -25,9 +25,6 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "upb/arena.h"
-
-#include "upb/alloc.h"
 #include "upb/internal/arena.h"
 
 // Must be last.
diff --git a/upb/array.c b/upb/array.c
index 2eaa43a851..3d3a8b8653 100644
--- a/upb/array.c
+++ b/upb/array.c
@@ -25,13 +25,10 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "upb/array.h"
+#include "upb/internal/array.h"
 
 #include <string.h>
 
-#include "upb/msg.h"
-#include "upb/msg_internal.h"
-
 // Must be last.
 #include "upb/port_def.inc"
 
diff --git a/upb/array.h b/upb/array.h
index c780fbe77a..7117392ed8 100644
--- a/upb/array.h
+++ b/upb/array.h
@@ -29,7 +29,6 @@
 #define UPB_ARRAY_H_
 
 #include "upb/message_value.h"
-#include "upb/upb.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/decode.c b/upb/decode.c
index 7f1e11effb..e55ee588bf 100644
--- a/upb/decode.c
+++ b/upb/decode.c
@@ -29,6 +29,7 @@
 
 #include <string.h>
 
+#include "upb/internal/array.h"
 #include "upb/internal/decode.h"
 #include "upb/upb.h"
 
diff --git a/upb/decode_fast.c b/upb/decode_fast.c
index f7748b1e92..30210b01b2 100644
--- a/upb/decode_fast.c
+++ b/upb/decode_fast.c
@@ -37,9 +37,10 @@
 
 #include "upb/decode_fast.h"
 
+#include "upb/internal/array.h"
 #include "upb/internal/decode.h"
 
-/* Must be last. */
+// Must be last.
 #include "upb/port_def.inc"
 
 #if UPB_FASTTABLE
diff --git a/upb/encode.c b/upb/encode.c
index 32565bddb2..fd6bdf32b0 100644
--- a/upb/encode.c
+++ b/upb/encode.c
@@ -29,14 +29,14 @@
 
 #include "upb/encode.h"
 
-#include <setjmp.h>
 #include <string.h>
 
 #include "upb/extension_registry.h"
+#include "upb/internal/array.h"
 #include "upb/msg_internal.h"
 #include "upb/upb.h"
 
-/* Must be last. */
+// Must be last.
 #include "upb/port_def.inc"
 
 #define UPB_PB_VARINT_MAX_LEN 10
diff --git a/upb/internal/array.c b/upb/internal/array.c
new file mode 100644
index 0000000000..41a0914ea7
--- /dev/null
+++ b/upb/internal/array.c
@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2009-2021, Google LLC
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of Google LLC nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL Google LLC BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "upb/internal/array.h"
+
+#include <string.h>
+
+// Must be last.
+#include "upb/port_def.inc"
+
+bool _upb_array_realloc(upb_Array* arr, size_t min_capacity, upb_Arena* arena) {
+  size_t new_capacity = UPB_MAX(arr->capacity, 4);
+  int elem_size_lg2 = arr->data & 7;
+  size_t old_bytes = arr->capacity << elem_size_lg2;
+  size_t new_bytes;
+  void* ptr = _upb_array_ptr(arr);
+
+  /* Log2 ceiling of size. */
+  while (new_capacity < min_capacity) new_capacity *= 2;
+
+  new_bytes = new_capacity << elem_size_lg2;
+  ptr = upb_Arena_Realloc(arena, ptr, old_bytes, new_bytes);
+
+  if (!ptr) {
+    return false;
+  }
+
+  arr->data = _upb_tag_arrptr(ptr, elem_size_lg2);
+  arr->capacity = new_capacity;
+  return true;
+}
+
+static upb_Array* getorcreate_array(upb_Array** arr_ptr, int elem_size_lg2,
+                                    upb_Arena* arena) {
+  upb_Array* arr = *arr_ptr;
+  if (!arr) {
+    arr = _upb_Array_New(arena, 4, elem_size_lg2);
+    if (!arr) return NULL;
+    *arr_ptr = arr;
+  }
+  return arr;
+}
+
+void* _upb_Array_Resize_fallback(upb_Array** arr_ptr, size_t size,
+                                 int elem_size_lg2, upb_Arena* arena) {
+  upb_Array* arr = getorcreate_array(arr_ptr, elem_size_lg2, arena);
+  return arr && _upb_Array_Resize(arr, size, arena) ? _upb_array_ptr(arr)
+                                                    : NULL;
+}
+
+bool _upb_Array_Append_fallback(upb_Array** arr_ptr, const void* value,
+                                int elem_size_lg2, upb_Arena* arena) {
+  upb_Array* arr = getorcreate_array(arr_ptr, elem_size_lg2, arena);
+  if (!arr) return false;
+
+  size_t elems = arr->size;
+
+  if (!_upb_Array_Resize(arr, elems + 1, arena)) {
+    return false;
+  }
+
+  char* data = _upb_array_ptr(arr);
+  memcpy(data + (elems << elem_size_lg2), value, 1 << elem_size_lg2);
+  return true;
+}
diff --git a/upb/internal/array.h b/upb/internal/array.h
new file mode 100644
index 0000000000..c3f96001bd
--- /dev/null
+++ b/upb/internal/array.h
@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2009-2021, Google LLC
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of Google LLC nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL Google LLC BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef UPB_INTERNAL_ARRAY_H_
+#define UPB_INTERNAL_ARRAY_H_
+
+#include <string.h>
+
+#include "upb/array.h"
+
+// Must be last.
+#include "upb/port_def.inc"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Our internal representation for repeated fields.  */
+struct upb_Array {
+  uintptr_t data;  /* Tagged ptr: low 3 bits of ptr are lg2(elem size). */
+  size_t size;     /* The number of elements in the array. */
+  size_t capacity; /* Allocated storage. Measured in elements. */
+  uint64_t junk;
+};
+
+UPB_INLINE const void* _upb_array_constptr(const upb_Array* arr) {
+  UPB_ASSERT((arr->data & 7) <= 4);
+  return (void*)(arr->data & ~(uintptr_t)7);
+}
+
+UPB_INLINE uintptr_t _upb_array_tagptr(void* ptr, int elem_size_lg2) {
+  UPB_ASSERT(elem_size_lg2 <= 4);
+  return (uintptr_t)ptr | elem_size_lg2;
+}
+
+UPB_INLINE void* _upb_array_ptr(upb_Array* arr) {
+  return (void*)_upb_array_constptr(arr);
+}
+
+UPB_INLINE uintptr_t _upb_tag_arrptr(void* ptr, int elem_size_lg2) {
+  UPB_ASSERT(elem_size_lg2 <= 4);
+  UPB_ASSERT(((uintptr_t)ptr & 7) == 0);
+  return (uintptr_t)ptr | (unsigned)elem_size_lg2;
+}
+
+UPB_INLINE upb_Array* _upb_Array_New(upb_Arena* a, size_t init_capacity,
+                                     int elem_size_lg2) {
+  const size_t arr_size = UPB_ALIGN_UP(sizeof(upb_Array), 8);
+  const size_t bytes = sizeof(upb_Array) + (init_capacity << elem_size_lg2);
+  upb_Array* arr = (upb_Array*)upb_Arena_Malloc(a, bytes);
+  if (!arr) return NULL;
+  arr->data = _upb_tag_arrptr(UPB_PTR_AT(arr, arr_size, void), elem_size_lg2);
+  arr->size = 0;
+  arr->capacity = init_capacity;
+  return arr;
+}
+
+/* Resizes the capacity of the array to be at least min_size. */
+bool _upb_array_realloc(upb_Array* arr, size_t min_size, upb_Arena* arena);
+
+/* Fallback functions for when the accessors require a resize. */
+void* _upb_Array_Resize_fallback(upb_Array** arr_ptr, size_t size,
+                                 int elem_size_lg2, upb_Arena* arena);
+bool _upb_Array_Append_fallback(upb_Array** arr_ptr, const void* value,
+                                int elem_size_lg2, upb_Arena* arena);
+
+UPB_INLINE bool _upb_array_reserve(upb_Array* arr, size_t size,
+                                   upb_Arena* arena) {
+  if (arr->capacity < size) return _upb_array_realloc(arr, size, arena);
+  return true;
+}
+
+UPB_INLINE bool _upb_Array_Resize(upb_Array* arr, size_t size,
+                                  upb_Arena* arena) {
+  if (!_upb_array_reserve(arr, size, arena)) return false;
+  arr->size = size;
+  return true;
+}
+
+UPB_INLINE void _upb_array_detach(const void* msg, size_t ofs) {
+  *UPB_PTR_AT(msg, ofs, upb_Array*) = NULL;
+}
+
+UPB_INLINE const void* _upb_array_accessor(const void* msg, size_t ofs,
+                                           size_t* size) {
+  const upb_Array* arr = *UPB_PTR_AT(msg, ofs, const upb_Array*);
+  if (arr) {
+    if (size) *size = arr->size;
+    return _upb_array_constptr(arr);
+  } else {
+    if (size) *size = 0;
+    return NULL;
+  }
+}
+
+UPB_INLINE void* _upb_array_mutable_accessor(void* msg, size_t ofs,
+                                             size_t* size) {
+  upb_Array* arr = *UPB_PTR_AT(msg, ofs, upb_Array*);
+  if (arr) {
+    if (size) *size = arr->size;
+    return _upb_array_ptr(arr);
+  } else {
+    if (size) *size = 0;
+    return NULL;
+  }
+}
+
+UPB_INLINE void* _upb_Array_Resize_accessor2(void* msg, size_t ofs, size_t size,
+                                             int elem_size_lg2,
+                                             upb_Arena* arena) {
+  upb_Array** arr_ptr = UPB_PTR_AT(msg, ofs, upb_Array*);
+  upb_Array* arr = *arr_ptr;
+  if (!arr || arr->capacity < size) {
+    return _upb_Array_Resize_fallback(arr_ptr, size, elem_size_lg2, arena);
+  }
+  arr->size = size;
+  return _upb_array_ptr(arr);
+}
+
+UPB_INLINE bool _upb_Array_Append_accessor2(void* msg, size_t ofs,
+                                            int elem_size_lg2,
+                                            const void* value,
+                                            upb_Arena* arena) {
+  upb_Array** arr_ptr = UPB_PTR_AT(msg, ofs, upb_Array*);
+  size_t elem_size = 1 << elem_size_lg2;
+  upb_Array* arr = *arr_ptr;
+  void* ptr;
+  if (!arr || arr->size == arr->capacity) {
+    return _upb_Array_Append_fallback(arr_ptr, value, elem_size_lg2, arena);
+  }
+  ptr = _upb_array_ptr(arr);
+  memcpy(UPB_PTR_AT(ptr, arr->size * elem_size, char), value, elem_size);
+  arr->size++;
+  return true;
+}
+
+/* Used by old generated code, remove once all code has been regenerated. */
+UPB_INLINE int _upb_sizelg2(upb_CType type) {
+  switch (type) {
+    case kUpb_CType_Bool:
+      return 0;
+    case kUpb_CType_Float:
+    case kUpb_CType_Int32:
+    case kUpb_CType_UInt32:
+    case kUpb_CType_Enum:
+      return 2;
+    case kUpb_CType_Message:
+      return UPB_SIZE(2, 3);
+    case kUpb_CType_Double:
+    case kUpb_CType_Int64:
+    case kUpb_CType_UInt64:
+      return 3;
+    case kUpb_CType_String:
+    case kUpb_CType_Bytes:
+      return UPB_SIZE(3, 4);
+  }
+  UPB_UNREACHABLE();
+}
+
+UPB_INLINE void* _upb_Array_Resize_accessor(void* msg, size_t ofs, size_t size,
+                                            upb_CType type, upb_Arena* arena) {
+  return _upb_Array_Resize_accessor2(msg, ofs, size, _upb_sizelg2(type), arena);
+}
+
+UPB_INLINE bool _upb_Array_Append_accessor(void* msg, size_t ofs,
+                                           size_t elem_size, upb_CType type,
+                                           const void* value,
+                                           upb_Arena* arena) {
+  (void)elem_size;
+  return _upb_Array_Append_accessor2(msg, ofs, _upb_sizelg2(type), value,
+                                     arena);
+}
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#include "upb/port_undef.inc"
+
+#endif /* UPB_INTERNAL_ARRAY_H_ */
diff --git a/upb/map.h b/upb/map.h
index ca8fccc0a2..ecaaa1d029 100644
--- a/upb/map.h
+++ b/upb/map.h
@@ -29,7 +29,6 @@
 #define UPB_MAP_H_
 
 #include "upb/message_value.h"
-#include "upb/upb.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/mini_table_accessors.c b/upb/mini_table_accessors.c
index c53a185849..1db65d8be0 100644
--- a/upb/mini_table_accessors.c
+++ b/upb/mini_table_accessors.c
@@ -29,8 +29,8 @@
 
 #include "upb/decode.h"
 #include "upb/encode.h"
+#include "upb/internal/array.h"
 #include "upb/mini_table.h"
-#include "upb/msg_internal.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/msg.c b/upb/msg.c
index 42225df7c2..ffc0f4f4d7 100644
--- a/upb/msg.c
+++ b/upb/msg.c
@@ -27,8 +27,9 @@
 
 #include "upb/msg.h"
 
-#include "upb/internal/table.h"
 #include "upb/msg_internal.h"
+
+// Must be last.
 #include "upb/port_def.inc"
 
 /** upb_Message ***************************************************************/
@@ -173,64 +174,6 @@ size_t upb_Message_ExtensionCount(const upb_Message* msg) {
   return count;
 }
 
-/** upb_Array *****************************************************************/
-
-bool _upb_array_realloc(upb_Array* arr, size_t min_capacity, upb_Arena* arena) {
-  size_t new_capacity = UPB_MAX(arr->capacity, 4);
-  int elem_size_lg2 = arr->data & 7;
-  size_t old_bytes = arr->capacity << elem_size_lg2;
-  size_t new_bytes;
-  void* ptr = _upb_array_ptr(arr);
-
-  /* Log2 ceiling of size. */
-  while (new_capacity < min_capacity) new_capacity *= 2;
-
-  new_bytes = new_capacity << elem_size_lg2;
-  ptr = upb_Arena_Realloc(arena, ptr, old_bytes, new_bytes);
-
-  if (!ptr) {
-    return false;
-  }
-
-  arr->data = _upb_tag_arrptr(ptr, elem_size_lg2);
-  arr->capacity = new_capacity;
-  return true;
-}
-
-static upb_Array* getorcreate_array(upb_Array** arr_ptr, int elem_size_lg2,
-                                    upb_Arena* arena) {
-  upb_Array* arr = *arr_ptr;
-  if (!arr) {
-    arr = _upb_Array_New(arena, 4, elem_size_lg2);
-    if (!arr) return NULL;
-    *arr_ptr = arr;
-  }
-  return arr;
-}
-
-void* _upb_Array_Resize_fallback(upb_Array** arr_ptr, size_t size,
-                                 int elem_size_lg2, upb_Arena* arena) {
-  upb_Array* arr = getorcreate_array(arr_ptr, elem_size_lg2, arena);
-  return arr && _upb_Array_Resize(arr, size, arena) ? _upb_array_ptr(arr)
-                                                    : NULL;
-}
-
-bool _upb_Array_Append_fallback(upb_Array** arr_ptr, const void* value,
-                                int elem_size_lg2, upb_Arena* arena) {
-  upb_Array* arr = getorcreate_array(arr_ptr, elem_size_lg2, arena);
-  if (!arr) return false;
-
-  size_t elems = arr->size;
-
-  if (!_upb_Array_Resize(arr, elems + 1, arena)) {
-    return false;
-  }
-
-  char* data = _upb_array_ptr(arr);
-  memcpy(data + (elems << elem_size_lg2), value, 1 << elem_size_lg2);
-  return true;
-}
-
 /** upb_Map *******************************************************************/
 
 upb_Map* _upb_Map_New(upb_Arena* a, size_t key_size, size_t value_size) {
diff --git a/upb/msg_internal.h b/upb/msg_internal.h
index 3ed032d5e0..a260b81842 100644
--- a/upb/msg_internal.h
+++ b/upb/msg_internal.h
@@ -406,162 +406,6 @@ UPB_INLINE bool _upb_has_submsg_nohasbit(const upb_Message* msg, size_t ofs) {
   return *UPB_PTR_AT(msg, ofs, const upb_Message*) != NULL;
 }
 
-/** upb_Array *****************************************************************/
-
-/* Our internal representation for repeated fields.  */
-struct upb_Array {
-  uintptr_t data;  /* Tagged ptr: low 3 bits of ptr are lg2(elem size). */
-  size_t size;     /* The number of elements in the array. */
-  size_t capacity; /* Allocated storage. Measured in elements. */
-  uint64_t junk;
-};
-
-UPB_INLINE const void* _upb_array_constptr(const upb_Array* arr) {
-  UPB_ASSERT((arr->data & 7) <= 4);
-  return (void*)(arr->data & ~(uintptr_t)7);
-}
-
-UPB_INLINE uintptr_t _upb_array_tagptr(void* ptr, int elem_size_lg2) {
-  UPB_ASSERT(elem_size_lg2 <= 4);
-  return (uintptr_t)ptr | elem_size_lg2;
-}
-
-UPB_INLINE void* _upb_array_ptr(upb_Array* arr) {
-  return (void*)_upb_array_constptr(arr);
-}
-
-UPB_INLINE uintptr_t _upb_tag_arrptr(void* ptr, int elem_size_lg2) {
-  UPB_ASSERT(elem_size_lg2 <= 4);
-  UPB_ASSERT(((uintptr_t)ptr & 7) == 0);
-  return (uintptr_t)ptr | (unsigned)elem_size_lg2;
-}
-
-UPB_INLINE upb_Array* _upb_Array_New(upb_Arena* a, size_t init_capacity,
-                                     int elem_size_lg2) {
-  const size_t arr_size = UPB_ALIGN_UP(sizeof(upb_Array), 8);
-  const size_t bytes = sizeof(upb_Array) + (init_capacity << elem_size_lg2);
-  upb_Array* arr = (upb_Array*)upb_Arena_Malloc(a, bytes);
-  if (!arr) return NULL;
-  arr->data = _upb_tag_arrptr(UPB_PTR_AT(arr, arr_size, void), elem_size_lg2);
-  arr->size = 0;
-  arr->capacity = init_capacity;
-  return arr;
-}
-
-/* Resizes the capacity of the array to be at least min_size. */
-bool _upb_array_realloc(upb_Array* arr, size_t min_size, upb_Arena* arena);
-
-/* Fallback functions for when the accessors require a resize. */
-void* _upb_Array_Resize_fallback(upb_Array** arr_ptr, size_t size,
-                                 int elem_size_lg2, upb_Arena* arena);
-bool _upb_Array_Append_fallback(upb_Array** arr_ptr, const void* value,
-                                int elem_size_lg2, upb_Arena* arena);
-
-UPB_INLINE bool _upb_array_reserve(upb_Array* arr, size_t size,
-                                   upb_Arena* arena) {
-  if (arr->capacity < size) return _upb_array_realloc(arr, size, arena);
-  return true;
-}
-
-UPB_INLINE bool _upb_Array_Resize(upb_Array* arr, size_t size,
-                                  upb_Arena* arena) {
-  if (!_upb_array_reserve(arr, size, arena)) return false;
-  arr->size = size;
-  return true;
-}
-
-UPB_INLINE void _upb_array_detach(const void* msg, size_t ofs) {
-  *UPB_PTR_AT(msg, ofs, upb_Array*) = NULL;
-}
-
-UPB_INLINE const void* _upb_array_accessor(const void* msg, size_t ofs,
-                                           size_t* size) {
-  const upb_Array* arr = *UPB_PTR_AT(msg, ofs, const upb_Array*);
-  if (arr) {
-    if (size) *size = arr->size;
-    return _upb_array_constptr(arr);
-  } else {
-    if (size) *size = 0;
-    return NULL;
-  }
-}
-
-UPB_INLINE void* _upb_array_mutable_accessor(void* msg, size_t ofs,
-                                             size_t* size) {
-  upb_Array* arr = *UPB_PTR_AT(msg, ofs, upb_Array*);
-  if (arr) {
-    if (size) *size = arr->size;
-    return _upb_array_ptr(arr);
-  } else {
-    if (size) *size = 0;
-    return NULL;
-  }
-}
-
-UPB_INLINE void* _upb_Array_Resize_accessor2(void* msg, size_t ofs, size_t size,
-                                             int elem_size_lg2,
-                                             upb_Arena* arena) {
-  upb_Array** arr_ptr = UPB_PTR_AT(msg, ofs, upb_Array*);
-  upb_Array* arr = *arr_ptr;
-  if (!arr || arr->capacity < size) {
-    return _upb_Array_Resize_fallback(arr_ptr, size, elem_size_lg2, arena);
-  }
-  arr->size = size;
-  return _upb_array_ptr(arr);
-}
-
-UPB_INLINE bool _upb_Array_Append_accessor2(void* msg, size_t ofs,
-                                            int elem_size_lg2,
-                                            const void* value,
-                                            upb_Arena* arena) {
-  upb_Array** arr_ptr = UPB_PTR_AT(msg, ofs, upb_Array*);
-  size_t elem_size = 1 << elem_size_lg2;
-  upb_Array* arr = *arr_ptr;
-  void* ptr;
-  if (!arr || arr->size == arr->capacity) {
-    return _upb_Array_Append_fallback(arr_ptr, value, elem_size_lg2, arena);
-  }
-  ptr = _upb_array_ptr(arr);
-  memcpy(UPB_PTR_AT(ptr, arr->size * elem_size, char), value, elem_size);
-  arr->size++;
-  return true;
-}
-
-/* Used by old generated code, remove once all code has been regenerated. */
-UPB_INLINE int _upb_sizelg2(upb_CType type) {
-  switch (type) {
-    case kUpb_CType_Bool:
-      return 0;
-    case kUpb_CType_Float:
-    case kUpb_CType_Int32:
-    case kUpb_CType_UInt32:
-    case kUpb_CType_Enum:
-      return 2;
-    case kUpb_CType_Message:
-      return UPB_SIZE(2, 3);
-    case kUpb_CType_Double:
-    case kUpb_CType_Int64:
-    case kUpb_CType_UInt64:
-      return 3;
-    case kUpb_CType_String:
-    case kUpb_CType_Bytes:
-      return UPB_SIZE(3, 4);
-  }
-  UPB_UNREACHABLE();
-}
-UPB_INLINE void* _upb_Array_Resize_accessor(void* msg, size_t ofs, size_t size,
-                                            upb_CType type, upb_Arena* arena) {
-  return _upb_Array_Resize_accessor2(msg, ofs, size, _upb_sizelg2(type), arena);
-}
-UPB_INLINE bool _upb_Array_Append_accessor(void* msg, size_t ofs,
-                                           size_t elem_size, upb_CType type,
-                                           const void* value,
-                                           upb_Arena* arena) {
-  (void)elem_size;
-  return _upb_Array_Append_accessor2(msg, ofs, _upb_sizelg2(type), value,
-                                     arena);
-}
-
 /** upb_Map *******************************************************************/
 
 /* Right now we use strmaps for everything.  We'll likely want to use
diff --git a/upbc/protoc-gen-upb.cc b/upbc/protoc-gen-upb.cc
index 5e6f8d209c..05f22fa36f 100644
--- a/upbc/protoc-gen-upb.cc
+++ b/upbc/protoc-gen-upb.cc
@@ -863,10 +863,11 @@ void WriteHeader(const FileLayout& layout, Output& output) {
   output(
       "#ifndef $0_UPB_H_\n"
       "#define $0_UPB_H_\n\n"
-      "#include \"upb/msg_internal.h\"\n"
       "#include \"upb/decode.h\"\n"
       "#include \"upb/decode_fast.h\"\n"
-      "#include \"upb/encode.h\"\n\n",
+      "#include \"upb/encode.h\"\n\n"
+      "#include \"upb/internal/array.h\"\n"
+      "#include \"upb/msg_internal.h\"\n",
       ToPreproc(file->name()));
 
   for (int i = 0; i < file->public_dependency_count(); i++) {
@@ -1480,6 +1481,7 @@ void WriteSource(const FileLayout& layout, Output& output,
 
   output(
       "#include <stddef.h>\n"
+      "#include \"upb/internal/array.h\"\n"
       "#include \"upb/msg_internal.h\"\n"
       "#include \"$0\"\n",
       HeaderFilename(file));