diff --git a/upb/message/accessors.c b/upb/message/accessors.c
index a3184a5a21..de142d90d4 100644
--- a/upb/message/accessors.c
+++ b/upb/message/accessors.c
@@ -24,10 +24,8 @@ bool upb_Message_SetMapEntry(upb_Map* map, const upb_MiniTable* m,
                              const upb_MiniTableField* f,
                              upb_Message* map_entry_message, upb_Arena* arena) {
   UPB_ASSERT(!upb_Message_IsFrozen(map_entry_message));
-
-  // TODO: use a variant of upb_MiniTable_GetSubMessageTable() here.
-  const upb_MiniTable* map_entry_mini_table = upb_MiniTableSub_Message(
-      m->UPB_PRIVATE(subs)[f->UPB_PRIVATE(submsg_index)]);
+  const upb_MiniTable* map_entry_mini_table =
+      upb_MiniTable_MapEntrySubMessage(m, f);
   UPB_ASSERT(map_entry_mini_table);
   const upb_MiniTableField* map_entry_key_field =
       upb_MiniTable_MapKey(map_entry_mini_table);
diff --git a/upb/message/accessors.h b/upb/message/accessors.h
index 59ec925d79..09ea66ae5b 100644
--- a/upb/message/accessors.h
+++ b/upb/message/accessors.h
@@ -22,9 +22,15 @@
 #include "upb/message/internal/message.h"
 #include "upb/message/internal/tagged_ptr.h"
 #include "upb/message/map.h"
+#include "upb/message/message.h"
 #include "upb/message/tagged_ptr.h"
 #include "upb/message/value.h"
 #include "upb/mini_table/enum.h"
+#include "upb/mini_table/extension.h"
+#include "upb/mini_table/field.h"
+#include "upb/mini_table/internal/field.h"
+#include "upb/mini_table/internal/message.h"
+#include "upb/mini_table/message.h"
 #include "upb/mini_table/sub.h"
 
 // Must be last.
@@ -354,8 +360,6 @@ UPB_API_INLINE void _upb_Message_SetTaggedMessagePtr(
   UPB_ASSUME(UPB_PRIVATE(_upb_MiniTableField_GetRep)(field) ==
              UPB_SIZE(kUpb_FieldRep_4Byte, kUpb_FieldRep_8Byte));
   UPB_ASSUME(upb_MiniTableField_IsScalar(field));
-  UPB_ASSERT(upb_MiniTableSub_Message(
-      mini_table->UPB_PRIVATE(subs)[field->UPB_PRIVATE(submsg_index)]));
   upb_Message_SetBaseField(msg, field, &sub_message);
 }
 
@@ -379,8 +383,8 @@ UPB_API_INLINE upb_Message* upb_Message_GetOrCreateMutableMessage(
   upb_Message* sub_message =
       *UPB_PTR_AT(msg, field->UPB_ONLYBITS(offset), upb_Message*);
   if (!sub_message) {
-    const upb_MiniTable* sub_mini_table = upb_MiniTableSub_Message(
-        mini_table->UPB_PRIVATE(subs)[field->UPB_PRIVATE(submsg_index)]);
+    const upb_MiniTable* sub_mini_table =
+        upb_MiniTable_SubMessage(mini_table, field);
     UPB_ASSERT(sub_mini_table);
     sub_message = _upb_Message_New(sub_mini_table, arena);
     *UPB_PTR_AT(msg, field->UPB_ONLYBITS(offset), upb_Message*) = sub_message;
diff --git a/upb/message/copy.c b/upb/message/copy.c
index 114b92e018..38cb8494bc 100644
--- a/upb/message/copy.c
+++ b/upb/message/copy.c
@@ -117,9 +117,8 @@ static upb_Map* upb_Message_Map_DeepClone(const upb_Map* map,
                                           const upb_MiniTableField* f,
                                           upb_Message* clone,
                                           upb_Arena* arena) {
-  // TODO: use a variant of upb_MiniTable_GetSubMessageTable() here.
-  const upb_MiniTable* map_entry_table = upb_MiniTableSub_Message(
-      mini_table->UPB_PRIVATE(subs)[f->UPB_PRIVATE(submsg_index)]);
+  const upb_MiniTable* map_entry_table =
+      upb_MiniTable_MapEntrySubMessage(mini_table, f);
   UPB_ASSERT(map_entry_table);
 
   const upb_MiniTableField* key_field = upb_MiniTable_MapKey(map_entry_table);
diff --git a/upb/message/promote.c b/upb/message/promote.c
index 51412e1781..d4b1ad1dee 100644
--- a/upb/message/promote.c
+++ b/upb/message/promote.c
@@ -327,12 +327,9 @@ upb_UnknownToMessage_Status upb_MiniTable_PromoteUnknownToMessageArray(
 upb_UnknownToMessage_Status upb_MiniTable_PromoteUnknownToMap(
     upb_Message* msg, const upb_MiniTable* mini_table,
     const upb_MiniTableField* field, int decode_options, upb_Arena* arena) {
-  // TODO: use a variant of upb_MiniTable_GetSubMessageTable() here.
-  const upb_MiniTable* map_entry_mini_table = upb_MiniTableSub_Message(
-      mini_table->UPB_PRIVATE(subs)[field->UPB_PRIVATE(submsg_index)]);
-  UPB_ASSERT(map_entry_mini_table);
+  const upb_MiniTable* map_entry_mini_table =
+      upb_MiniTable_MapEntrySubMessage(mini_table, field);
   UPB_ASSERT(upb_MiniTable_FieldCount(map_entry_mini_table) == 2);
-  UPB_ASSERT(upb_MiniTableField_IsMap(field));
   // Find all unknowns with given field number and parse.
   upb_FindUnknownRet unknown;
   while (1) {
diff --git a/upb/mini_descriptor/internal/encode_test.cc b/upb/mini_descriptor/internal/encode_test.cc
index 3ae2f6f56c..a84c739bbc 100644
--- a/upb/mini_descriptor/internal/encode_test.cc
+++ b/upb/mini_descriptor/internal/encode_test.cc
@@ -45,7 +45,7 @@ TEST_P(MiniTableTest, Empty) {
   upb_MiniTable* table =
       _upb_MiniTable_Build(nullptr, 0, GetParam(), arena.ptr(), status.ptr());
   ASSERT_NE(nullptr, table);
-  EXPECT_EQ(0, table->UPB_PRIVATE(field_count));
+  EXPECT_EQ(0, upb_MiniTable_FieldCount(table));
   EXPECT_EQ(0, table->UPB_PRIVATE(required_count));
 }
 
@@ -242,11 +242,11 @@ TEST_P(MiniTableTest, SubsInitializedToEmpty) {
   upb_MiniTable* table = _upb_MiniTable_Build(
       e.data().data(), e.data().size(), GetParam(), arena.ptr(), status.ptr());
   ASSERT_NE(nullptr, table);
-  EXPECT_EQ(table->UPB_PRIVATE(field_count), 2);
-  EXPECT_TRUE(UPB_PRIVATE(_upb_MiniTable_IsEmpty)(
-      upb_MiniTableSub_Message(table->UPB_PRIVATE(subs)[0])));
-  EXPECT_TRUE(UPB_PRIVATE(_upb_MiniTable_IsEmpty)(
-      upb_MiniTableSub_Message(table->UPB_PRIVATE(subs)[1])));
+  EXPECT_EQ(upb_MiniTable_FieldCount(table), 2);
+  EXPECT_FALSE(upb_MiniTable_FieldIsLinked(
+      table, upb_MiniTable_GetFieldByIndex(table, 0)));
+  EXPECT_FALSE(upb_MiniTable_FieldIsLinked(
+      table, upb_MiniTable_GetFieldByIndex(table, 1)));
 }
 
 TEST(MiniTableEnumTest, PositiveAndNegative) {
diff --git a/upb/mini_table/internal/message.h b/upb/mini_table/internal/message.h
index e044c0e48c..d5b1ae4e0b 100644
--- a/upb/mini_table/internal/message.h
+++ b/upb/mini_table/internal/message.h
@@ -8,8 +8,10 @@
 #ifndef UPB_MINI_TABLE_INTERNAL_MESSAGE_H_
 #define UPB_MINI_TABLE_INTERNAL_MESSAGE_H_
 
+#include <stddef.h>
 #include <stdint.h>
 
+#include "upb/base/descriptor_constants.h"
 #include "upb/mini_table/internal/field.h"
 #include "upb/mini_table/internal/sub.h"
 
@@ -97,34 +99,44 @@ UPB_API_INLINE const struct upb_MiniTableField* upb_MiniTable_GetFieldByIndex(
   return &m->UPB_ONLYBITS(fields)[i];
 }
 
-UPB_INLINE const union upb_MiniTableSub* UPB_PRIVATE(
+UPB_INLINE const union upb_MiniTableSub UPB_PRIVATE(
     _upb_MiniTable_GetSubByIndex)(const struct upb_MiniTable* m, uint32_t i) {
-  return &m->UPB_PRIVATE(subs)[i];
+  return m->UPB_PRIVATE(subs)[i];
+}
+
+UPB_API_INLINE const struct upb_MiniTable* upb_MiniTable_SubMessage(
+    const struct upb_MiniTable* m, const struct upb_MiniTableField* f) {
+  if (upb_MiniTableField_CType(f) != kUpb_CType_Message) {
+    return NULL;
+  }
+  return m->UPB_PRIVATE(subs)[f->UPB_PRIVATE(submsg_index)].UPB_PRIVATE(submsg);
 }
 
 UPB_API_INLINE const struct upb_MiniTable* upb_MiniTable_GetSubMessageTable(
     const struct upb_MiniTable* m, const struct upb_MiniTableField* f) {
-  UPB_ASSERT(upb_MiniTableField_CType(f) == kUpb_CType_Message);
-  const struct upb_MiniTable* ret = upb_MiniTableSub_Message(
-      m->UPB_PRIVATE(subs)[f->UPB_PRIVATE(submsg_index)]);
+  UPB_ASSUME(upb_MiniTableField_CType(f) == kUpb_CType_Message);
+  const struct upb_MiniTable* ret = upb_MiniTable_SubMessage(m, f);
   UPB_ASSUME(ret);
   return UPB_PRIVATE(_upb_MiniTable_IsEmpty)(ret) ? NULL : ret;
 }
 
-UPB_API_INLINE const struct upb_MiniTable* upb_MiniTable_SubMessage(
+UPB_API_INLINE bool upb_MiniTable_FieldIsLinked(
     const struct upb_MiniTable* m, const struct upb_MiniTableField* f) {
-  if (upb_MiniTableField_CType(f) != kUpb_CType_Message) {
-    return NULL;
-  }
-  return upb_MiniTableSub_Message(
-      m->UPB_PRIVATE(subs)[f->UPB_PRIVATE(submsg_index)]);
+  return upb_MiniTable_GetSubMessageTable(m, f) != NULL;
+}
+
+UPB_API_INLINE const struct upb_MiniTable* upb_MiniTable_MapEntrySubMessage(
+    const struct upb_MiniTable* m, const struct upb_MiniTableField* f) {
+  UPB_ASSERT(upb_MiniTable_FieldIsLinked(m, f));  // Map entries must be linked.
+  UPB_ASSERT(upb_MiniTableField_IsMap(f));        // Function precondition.
+  return upb_MiniTable_SubMessage(m, f);
 }
 
 UPB_API_INLINE const struct upb_MiniTableEnum* upb_MiniTable_GetSubEnumTable(
     const struct upb_MiniTable* m, const struct upb_MiniTableField* f) {
   UPB_ASSERT(upb_MiniTableField_CType(f) == kUpb_CType_Enum);
-  return upb_MiniTableSub_Enum(
-      m->UPB_PRIVATE(subs)[f->UPB_PRIVATE(submsg_index)]);
+  return m->UPB_PRIVATE(subs)[f->UPB_PRIVATE(submsg_index)].UPB_PRIVATE(
+      subenum);
 }
 
 UPB_API_INLINE const struct upb_MiniTableField* upb_MiniTable_MapKey(
@@ -143,11 +155,6 @@ UPB_API_INLINE const struct upb_MiniTableField* upb_MiniTable_MapValue(
   return f;
 }
 
-UPB_API_INLINE bool upb_MiniTable_FieldIsLinked(
-    const struct upb_MiniTable* m, const struct upb_MiniTableField* f) {
-  return upb_MiniTable_GetSubMessageTable(m, f) != NULL;
-}
-
 // Computes a bitmask in which the |m->required_count| lowest bits are set.
 //
 // Sample output:
diff --git a/upb/mini_table/message.h b/upb/mini_table/message.h
index 1ce9087b0a..6589762f4e 100644
--- a/upb/mini_table/message.h
+++ b/upb/mini_table/message.h
@@ -34,10 +34,20 @@ UPB_API_INLINE int upb_MiniTable_FieldCount(const upb_MiniTable* m);
 UPB_API_INLINE const upb_MiniTable* upb_MiniTable_GetSubMessageTable(
     const upb_MiniTable* m, const upb_MiniTableField* f);
 
-// Returns the MiniTable for a message field if it is a submessage.
+// Returns the MiniTable for a message field if it is a submessage, otherwise
+// returns NULL.
+//
+// WARNING: if dynamic tree shaking is in use, the return value may be the
+// "empty", zero-field placeholder message instead of the real message type.
+// If the message is later linked, this function will begin returning the real
+// message type.
 UPB_API_INLINE const upb_MiniTable* upb_MiniTable_SubMessage(
     const upb_MiniTable* m, const upb_MiniTableField* f);
 
+// Returns the MiniTable for a map field.  The given field must refer to a map.
+UPB_API_INLINE const upb_MiniTable* upb_MiniTable_MapEntrySubMessage(
+    const upb_MiniTable* m, const upb_MiniTableField* f);
+
 // Returns the MiniTableEnum for a message field, NULL if the field is unlinked.
 UPB_API_INLINE const upb_MiniTableEnum* upb_MiniTable_GetSubEnumTable(
     const upb_MiniTable* m, const upb_MiniTableField* f);