diff --git a/upb/BUILD b/upb/BUILD
index e1ab3447ec..07d6de32a8 100644
--- a/upb/BUILD
+++ b/upb/BUILD
@@ -210,6 +210,8 @@ bootstrap_cc_library(
         "upb/reflection/extension_range.c",
         "upb/reflection/field_def.c",
         "upb/reflection/file_def.c",
+        "upb/reflection/internal/strdup2.c",
+        "upb/reflection/internal/strdup2.h",
         "upb/reflection/message.c",
         "upb/reflection/message_def.c",
         "upb/reflection/message_reserved_range.c",
diff --git a/upb/upb/base/internal/log2.h b/upb/upb/base/internal/log2.h
index 399c474897..3d5f381d5a 100644
--- a/upb/upb/base/internal/log2.h
+++ b/upb/upb/base/internal/log2.h
@@ -6,8 +6,8 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-#ifndef UPB_BASE_LOG2_H_
-#define UPB_BASE_LOG2_H_
+#ifndef UPB_BASE_INTERNAL_LOG2_H_
+#define UPB_BASE_INTERNAL_LOG2_H_
 
 // Must be last.
 #include "upb/upb/port/def.inc"
@@ -35,4 +35,4 @@ UPB_INLINE int upb_Log2CeilingSize(int x) { return 1 << upb_Log2Ceiling(x); }
 
 #include "upb/upb/port/undef.inc"
 
-#endif /* UPB_BASE_LOG2_H_ */
+#endif /* UPB_BASE_INTERNAL_LOG2_H_ */
diff --git a/upb/upb/hash/common.c b/upb/upb/hash/common.c
index 7eecaa0c75..79c165011f 100644
--- a/upb/upb/hash/common.c
+++ b/upb/upb/hash/common.c
@@ -72,23 +72,6 @@ static int log2ceil(uint64_t v) {
   return UPB_MIN(UPB_MAXARRSIZE, ret);
 }
 
-char* upb_strdup2(const char* s, size_t len, upb_Arena* a) {
-  size_t n;
-  char* p;
-
-  /* Prevent overflow errors. */
-  if (len == SIZE_MAX) return NULL;
-  /* Always null-terminate, even if binary data; but don't rely on the input to
-   * have a null-terminating byte since it may be a raw binary buffer. */
-  n = len + 1;
-  p = upb_Arena_Malloc(a, n);
-  if (p) {
-    if (len != 0) memcpy(p, s, len);
-    p[len] = 0;
-  }
-  return p;
-}
-
 /* A type to represent the lookup key of either a strtable or an inttable. */
 typedef union {
   uintptr_t num;
diff --git a/upb/upb/hash/common.h b/upb/upb/hash/common.h
index 44588b045b..51eb1bf951 100644
--- a/upb/upb/hash/common.h
+++ b/upb/upb/hash/common.h
@@ -68,10 +68,6 @@ typedef struct {
   uint64_t val;
 } upb_value;
 
-/* Variant that works with a length-delimited rather than NULL-delimited string,
- * as supported by strtable. */
-char* upb_strdup2(const char* s, size_t len, upb_Arena* a);
-
 UPB_INLINE void _upb_value_setval(upb_value* v, uint64_t val) { v->val = val; }
 
 /* For each value ctype, define the following set of functions:
diff --git a/upb/upb/reflection/def_builder.c b/upb/upb/reflection/def_builder.c
index da502f356f..f73fd3da89 100644
--- a/upb/upb/reflection/def_builder.c
+++ b/upb/upb/reflection/def_builder.c
@@ -35,6 +35,7 @@
 #include "upb/upb/reflection/def_pool.h"
 #include "upb/upb/reflection/def_type.h"
 #include "upb/upb/reflection/field_def.h"
+#include "upb/upb/reflection/internal/strdup2.h"
 
 // Must be last.
 #include "upb/upb/port/def.inc"
diff --git a/upb/upb/reflection/enum_def.c b/upb/upb/reflection/enum_def.c
index 5adf9842bd..1e34daae86 100644
--- a/upb/upb/reflection/enum_def.c
+++ b/upb/upb/reflection/enum_def.c
@@ -40,6 +40,7 @@
 #include "upb/upb/reflection/internal/enum_value_def.h"
 #include "upb/upb/reflection/internal/file_def.h"
 #include "upb/upb/reflection/internal/message_def.h"
+#include "upb/upb/reflection/internal/strdup2.h"
 
 // Must be last.
 #include "upb/upb/port/def.inc"
diff --git a/upb/upb/reflection/field_def.c b/upb/upb/reflection/field_def.c
index dc6ab1f3c8..4c87ca3d07 100644
--- a/upb/upb/reflection/field_def.c
+++ b/upb/upb/reflection/field_def.c
@@ -45,6 +45,7 @@
 #include "upb/upb/reflection/internal/file_def.h"
 #include "upb/upb/reflection/internal/message_def.h"
 #include "upb/upb/reflection/internal/oneof_def.h"
+#include "upb/upb/reflection/internal/strdup2.h"
 
 // Must be last.
 #include "upb/upb/port/def.inc"
diff --git a/upb/upb/reflection/file_def.c b/upb/upb/reflection/file_def.c
index 5a4fab37ed..7b9ddf9276 100644
--- a/upb/upb/reflection/file_def.c
+++ b/upb/upb/reflection/file_def.c
@@ -36,6 +36,7 @@
 #include "upb/upb/reflection/internal/field_def.h"
 #include "upb/upb/reflection/internal/message_def.h"
 #include "upb/upb/reflection/internal/service_def.h"
+#include "upb/upb/reflection/internal/strdup2.h"
 
 // Must be last.
 #include "upb/upb/port/def.inc"
diff --git a/upb/upb/reflection/internal/strdup2.c b/upb/upb/reflection/internal/strdup2.c
new file mode 100644
index 0000000000..54de9bed6c
--- /dev/null
+++ b/upb/upb/reflection/internal/strdup2.c
@@ -0,0 +1,56 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google LLC.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// 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 THE COPYRIGHT
+// OWNER OR CONTRIBUTORS 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/upb/reflection/internal/strdup2.h"
+
+#include <string.h>
+
+#include "upb/upb/mem/arena.h"
+
+// Must be last.
+#include "upb/upb/port/def.inc"
+
+char* upb_strdup2(const char* s, size_t len, upb_Arena* a) {
+  size_t n;
+  char* p;
+
+  // Prevent overflow errors.
+  if (len == SIZE_MAX) return NULL;
+
+  // Always null-terminate, even if binary data; but don't rely on the input to
+  // have a null-terminating byte since it may be a raw binary buffer.
+  n = len + 1;
+  p = upb_Arena_Malloc(a, n);
+  if (p) {
+    if (len != 0) memcpy(p, s, len);
+    p[len] = 0;
+  }
+  return p;
+}
diff --git a/upb/upb/reflection/internal/strdup2.h b/upb/upb/reflection/internal/strdup2.h
new file mode 100644
index 0000000000..845e8f076e
--- /dev/null
+++ b/upb/upb/reflection/internal/strdup2.h
@@ -0,0 +1,55 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google LLC.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// 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 THE COPYRIGHT
+// OWNER OR CONTRIBUTORS 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_REFLECTION_INTERNAL_STRDUP2_H_
+#define UPB_REFLECTION_INTERNAL_STRDUP2_H_
+
+#include <stddef.h>
+
+#include "upb/upb/mem/arena.h"
+
+// Must be last.
+#include "upb/upb/port/def.inc"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Variant that works with a length-delimited rather than NULL-delimited string,
+// as supported by strtable.
+char* upb_strdup2(const char* s, size_t len, upb_Arena* a);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#include "upb/upb/port/undef.inc"
+
+#endif /* UPB_REFLECTION_INTERNAL_STRDUP2_H_ */
diff --git a/upb/upb/reflection/message_def.c b/upb/upb/reflection/message_def.c
index 0cde9a3121..35fe6d844c 100644
--- a/upb/upb/reflection/message_def.c
+++ b/upb/upb/reflection/message_def.c
@@ -44,6 +44,7 @@
 #include "upb/upb/reflection/internal/file_def.h"
 #include "upb/upb/reflection/internal/message_reserved_range.h"
 #include "upb/upb/reflection/internal/oneof_def.h"
+#include "upb/upb/reflection/internal/strdup2.h"
 
 // Must be last.
 #include "upb/upb/port/def.inc"