diff --git a/upb/base/BUILD b/upb/base/BUILD
index 2fce94baf5335..c1ab1d3321a8c 100644
--- a/upb/base/BUILD
+++ b/upb/base/BUILD
@@ -29,6 +29,7 @@ cc_library(
 cc_library(
     name = "internal",
     hdrs = [
+        "internal/endian.h",
         "internal/log2.h",
     ],
     copts = UPB_DEFAULT_COPTS,
diff --git a/upb/wire/internal/endian.h b/upb/base/internal/endian.h
similarity index 53%
rename from upb/wire/internal/endian.h
rename to upb/base/internal/endian.h
index 09788c9b313dc..089742752673e 100644
--- a/upb/wire/internal/endian.h
+++ b/upb/base/internal/endian.h
@@ -5,8 +5,8 @@
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 
-#ifndef UPB_WIRE_INTERNAL_ENDIAN_H_
-#define UPB_WIRE_INTERNAL_ENDIAN_H_
+#ifndef UPB_BASE_INTERNAL_ENDIAN_H_
+#define UPB_BASE_INTERNAL_ENDIAN_H_
 
 #include <stdint.h>
 
@@ -17,23 +17,24 @@
 extern "C" {
 #endif
 
-UPB_INLINE bool UPB_PRIVATE(_upb_IsLittleEndian)(void) {
+UPB_INLINE bool upb_IsLittleEndian(void) {
   const int x = 1;
   return *(char*)&x == 1;
 }
 
-UPB_INLINE uint32_t UPB_PRIVATE(_upb_BigEndian32)(uint32_t val) {
-  if (UPB_PRIVATE(_upb_IsLittleEndian)()) return val;
+UPB_INLINE uint32_t upb_BigEndian32(uint32_t val) {
+  if (upb_IsLittleEndian()) return val;
 
   return ((val & 0xff) << 24) | ((val & 0xff00) << 8) |
          ((val & 0xff0000) >> 8) | ((val & 0xff000000) >> 24);
 }
 
-UPB_INLINE uint64_t UPB_PRIVATE(_upb_BigEndian64)(uint64_t val) {
-  if (UPB_PRIVATE(_upb_IsLittleEndian)()) return val;
+UPB_INLINE uint64_t upb_BigEndian64(uint64_t val) {
+  if (upb_IsLittleEndian()) return val;
 
-  return ((uint64_t)UPB_PRIVATE(_upb_BigEndian32)((uint32_t)val) << 32) |
-         UPB_PRIVATE(_upb_BigEndian32)((uint32_t)(val >> 32));
+  const uint64_t hi = ((uint64_t)upb_BigEndian32((uint32_t)val)) << 32;
+  const uint64_t lo = upb_BigEndian32((uint32_t)(val >> 32));
+  return hi | lo;
 }
 
 #ifdef __cplusplus
@@ -42,4 +43,4 @@ UPB_INLINE uint64_t UPB_PRIVATE(_upb_BigEndian64)(uint64_t val) {
 
 #include "upb/port/undef.inc"
 
-#endif /* UPB_WIRE_INTERNAL_ENDIAN_H_ */
+#endif /* UPB_BASE_INTERNAL_ENDIAN_H_ */
diff --git a/upb/util/BUILD b/upb/util/BUILD
index e43b23959c530..b508a5f183562 100644
--- a/upb/util/BUILD
+++ b/upb/util/BUILD
@@ -165,6 +165,7 @@ cc_test(
         ":compare",
         "//upb:port",
         "//upb:wire_reader",
+        "//upb/base:internal",
         "@com_google_absl//absl/strings",
         "@com_google_googletest//:gtest",
         "@com_google_googletest//:gtest_main",
diff --git a/upb/util/compare_test.cc b/upb/util/compare_test.cc
index b29a0ccbdce66..1a1a2935d0932 100644
--- a/upb/util/compare_test.cc
+++ b/upb/util/compare_test.cc
@@ -15,7 +15,7 @@
 #include <vector>
 
 #include <gtest/gtest.h>
-#include "upb/wire/internal/endian.h"
+#include "upb/base/internal/endian.h"
 #include "upb/wire/types.h"
 
 // Must be last.
@@ -84,11 +84,11 @@ std::string ToBinaryPayload(const UnknownFields& fields) {
       ret.append(val->val);
     } else if (const auto* val = std::get_if<Fixed64>(&field.value)) {
       EncodeVarint(field.field_number << 3 | kUpb_WireType_64Bit, &ret);
-      uint64_t swapped = UPB_PRIVATE(_upb_BigEndian64)(val->val);
+      uint64_t swapped = upb_BigEndian64(val->val);
       ret.append(reinterpret_cast<const char*>(&swapped), sizeof(swapped));
     } else if (const auto* val = std::get_if<Fixed32>(&field.value)) {
       EncodeVarint(field.field_number << 3 | kUpb_WireType_32Bit, &ret);
-      uint32_t swapped = UPB_PRIVATE(_upb_BigEndian32)(val->val);
+      uint32_t swapped = upb_BigEndian32(val->val);
       ret.append(reinterpret_cast<const char*>(&swapped), sizeof(swapped));
     } else if (const auto* val = std::get_if<Group>(&field.value)) {
       EncodeVarint(field.field_number << 3 | kUpb_WireType_StartGroup, &ret);
diff --git a/upb/wire/BUILD b/upb/wire/BUILD
index 93be09bd9fee8..891ed03d9cfcb 100644
--- a/upb/wire/BUILD
+++ b/upb/wire/BUILD
@@ -14,6 +14,7 @@ cc_library(
         "encode.c",
         "internal/constants.h",
         "internal/decode_fast.c",
+        "internal/decoder.c",
         "internal/decoder.h",
     ],
     hdrs = [
@@ -34,6 +35,7 @@ cc_library(
         "//upb:message_accessors",
         "//upb:mini_table",
         "//upb:port",
+        "//upb/base:internal",
         "//upb/mem:internal",
         "//upb/message:internal",
         "//upb/mini_table:internal",
@@ -43,11 +45,10 @@ cc_library(
 cc_library(
     name = "reader",
     srcs = [
+        "internal/reader.h",
         "reader.c",
     ],
     hdrs = [
-        "internal/endian.h",
-        "internal/reader.h",
         "reader.h",
         "types.h",
     ],
@@ -55,6 +56,7 @@ cc_library(
     deps = [
         ":eps_copy_input_stream",
         "//upb:port",
+        "//upb/base:internal",
     ],
 )
 
diff --git a/upb/wire/decode.c b/upb/wire/decode.c
index a80f65c11c9ea..6d52b3702e948 100644
--- a/upb/wire/decode.c
+++ b/upb/wire/decode.c
@@ -14,6 +14,7 @@
 #include <string.h>
 
 #include "upb/base/descriptor_constants.h"
+#include "upb/base/internal/endian.h"
 #include "upb/base/string_view.h"
 #include "upb/hash/common.h"
 #include "upb/mem/arena.h"
@@ -42,7 +43,6 @@
 #include "upb/wire/eps_copy_input_stream.h"
 #include "upb/wire/internal/constants.h"
 #include "upb/wire/internal/decoder.h"
-#include "upb/wire/internal/endian.h"
 #include "upb/wire/reader.h"
 
 // Must be last.
@@ -212,7 +212,7 @@ static const char* upb_Decoder_DecodeSize(upb_Decoder* d, const char* ptr,
 }
 
 static void _upb_Decoder_MungeInt32(wireval* val) {
-  if (!UPB_PRIVATE(_upb_IsLittleEndian)()) {
+  if (!upb_IsLittleEndian()) {
     /* The next stage will memcpy(dst, &val, 4) */
     val->uint32_val = val->uint64_val;
   }
@@ -434,7 +434,7 @@ static const char* _upb_Decoder_DecodeFixedPacked(
   arr->UPB_PRIVATE(size) += count;
   // Note: if/when the decoder supports multi-buffer input, we will need to
   // handle buffer seams here.
-  if (UPB_PRIVATE(_upb_IsLittleEndian)()) {
+  if (upb_IsLittleEndian()) {
     ptr = upb_EpsCopyInputStream_Copy(&d->input, ptr, mem, val->size);
   } else {
     int delta = upb_EpsCopyInputStream_PushLimit(&d->input, ptr, val->size);
@@ -758,7 +758,7 @@ const char* _upb_Decoder_CheckRequired(upb_Decoder* d, const char* ptr,
   }
   uint64_t msg_head;
   memcpy(&msg_head, msg, 8);
-  msg_head = UPB_PRIVATE(_upb_BigEndian64)(msg_head);
+  msg_head = upb_BigEndian64(msg_head);
   if (UPB_PRIVATE(_upb_MiniTable_RequiredMask)(m) & ~msg_head) {
     d->missing_required = true;
   }
diff --git a/upb/wire/encode.c b/upb/wire/encode.c
index 5797e97ec1f70..aeec7edec3928 100644
--- a/upb/wire/encode.c
+++ b/upb/wire/encode.c
@@ -15,6 +15,7 @@
 #include <string.h>
 
 #include "upb/base/descriptor_constants.h"
+#include "upb/base/internal/endian.h"
 #include "upb/base/string_view.h"
 #include "upb/hash/common.h"
 #include "upb/hash/str_table.h"
@@ -37,7 +38,6 @@
 #include "upb/mini_table/message.h"
 #include "upb/mini_table/sub.h"
 #include "upb/wire/internal/constants.h"
-#include "upb/wire/internal/endian.h"
 #include "upb/wire/types.h"
 
 // Must be last.
@@ -130,12 +130,12 @@ static void encode_bytes(upb_encstate* e, const void* data, size_t len) {
 }
 
 static void encode_fixed64(upb_encstate* e, uint64_t val) {
-  val = UPB_PRIVATE(_upb_BigEndian64)(val);
+  val = upb_BigEndian64(val);
   encode_bytes(e, &val, sizeof(uint64_t));
 }
 
 static void encode_fixed32(upb_encstate* e, uint32_t val) {
-  val = UPB_PRIVATE(_upb_BigEndian32)(val);
+  val = upb_BigEndian32(val);
   encode_bytes(e, &val, sizeof(uint32_t));
 }
 
@@ -186,18 +186,18 @@ static void encode_fixedarray(upb_encstate* e, const upb_Array* arr,
   const char* data = _upb_array_constptr(arr);
   const char* ptr = data + bytes - elem_size;
 
-  if (tag || !UPB_PRIVATE(_upb_IsLittleEndian)()) {
+  if (tag || !upb_IsLittleEndian()) {
     while (true) {
       if (elem_size == 4) {
         uint32_t val;
         memcpy(&val, ptr, sizeof(val));
-        val = UPB_PRIVATE(_upb_BigEndian32)(val);
+        val = upb_BigEndian32(val);
         encode_bytes(e, &val, elem_size);
       } else {
         UPB_ASSERT(elem_size == 8);
         uint64_t val;
         memcpy(&val, ptr, sizeof(val));
-        val = UPB_PRIVATE(_upb_BigEndian64)(val);
+        val = upb_BigEndian64(val);
         encode_bytes(e, &val, elem_size);
       }
 
@@ -552,7 +552,7 @@ static void encode_message(upb_encstate* e, const upb_Message* msg,
       m->UPB_PRIVATE(required_count)) {
     uint64_t msg_head;
     memcpy(&msg_head, msg, 8);
-    msg_head = UPB_PRIVATE(_upb_BigEndian64)(msg_head);
+    msg_head = upb_BigEndian64(msg_head);
     if (UPB_PRIVATE(_upb_MiniTable_RequiredMask)(m) & ~msg_head) {
       encode_err(e, kUpb_EncodeStatus_MissingRequired);
     }
diff --git a/upb/wire/internal/decode_fast.h b/upb/wire/internal/decode_fast.h
index 5f486297196f0..53270f82eae66 100644
--- a/upb/wire/internal/decode_fast.h
+++ b/upb/wire/internal/decode_fast.h
@@ -39,8 +39,8 @@
 //   - '1' for one-byte tags (field numbers 1-15)
 //   - '2' for two-byte tags (field numbers 16-2048)
 
-#ifndef UPB_WIRE_DECODE_INTERNAL_FAST_H_
-#define UPB_WIRE_DECODE_INTERNAL_FAST_H_
+#ifndef UPB_WIRE_INTERNAL_DECODE_FAST_H_
+#define UPB_WIRE_INTERNAL_DECODE_FAST_H_
 
 #include "upb/message/message.h"
 
@@ -110,6 +110,7 @@ TAGBYTES(o)
 TAGBYTES(r)
 
 #undef F
+#undef UTF8
 #undef TAGBYTES
 
 /* sub-message fields *********************************************************/
@@ -132,9 +133,9 @@ TAGBYTES(s)
 TAGBYTES(o)
 TAGBYTES(r)
 
-#undef TAGBYTES
-#undef SIZES
 #undef F
+#undef SIZES
+#undef TAGBYTES
 
 #undef UPB_PARSE_PARAMS
 
@@ -144,4 +145,4 @@ TAGBYTES(r)
 
 #include "upb/port/undef.inc"
 
-#endif /* UPB_WIRE_DECODE_INTERNAL_FAST_H_ */
+#endif /* UPB_WIRE_INTERNAL_DECODE_FAST_H_ */
diff --git a/upb/wire/internal/decoder.c b/upb/wire/internal/decoder.c
new file mode 100644
index 0000000000000..f4ec76770ddba
--- /dev/null
+++ b/upb/wire/internal/decoder.c
@@ -0,0 +1,31 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google LLC.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#include "upb/wire/internal/decoder.h"
+
+#include "upb/message/internal/message.h"
+#include "upb/wire/decode.h"
+#include "upb/wire/eps_copy_input_stream.h"
+
+// Must be last.
+#include "upb/port/def.inc"
+
+const char* _upb_Decoder_BufferFlipCallback(upb_EpsCopyInputStream* e,
+                                            const char* old_end,
+                                            const char* new_start) {
+  upb_Decoder* d = (upb_Decoder*)e;
+  if (!old_end) _upb_FastDecoder_ErrorJmp(d, kUpb_DecodeStatus_Malformed);
+
+  if (d->unknown) {
+    if (!UPB_PRIVATE(_upb_Message_AddUnknown)(
+            d->unknown_msg, d->unknown, old_end - d->unknown, &d->arena)) {
+      _upb_FastDecoder_ErrorJmp(d, kUpb_DecodeStatus_OutOfMemory);
+    }
+    d->unknown = new_start;
+  }
+  return new_start;
+}
diff --git a/upb/wire/internal/decoder.h b/upb/wire/internal/decoder.h
index 5ca1e1b2b2a8e..e2d418508ccab 100644
--- a/upb/wire/internal/decoder.h
+++ b/upb/wire/internal/decoder.h
@@ -55,8 +55,6 @@ typedef struct upb_Decoder {
  * noreturn. */
 const char* _upb_FastDecoder_ErrorJmp(upb_Decoder* d, int status);
 
-extern const uint8_t upb_utf8_offsets[];
-
 UPB_INLINE
 bool _upb_Decoder_VerifyUtf8Inline(const char* ptr, int len) {
   return utf8_range_IsValid(ptr, len);
@@ -84,20 +82,9 @@ UPB_INLINE bool _upb_Decoder_IsDone(upb_Decoder* d, const char** ptr) {
       &d->input, ptr, &_upb_Decoder_IsDoneFallback);
 }
 
-UPB_INLINE const char* _upb_Decoder_BufferFlipCallback(
-    upb_EpsCopyInputStream* e, const char* old_end, const char* new_start) {
-  upb_Decoder* d = (upb_Decoder*)e;
-  if (!old_end) _upb_FastDecoder_ErrorJmp(d, kUpb_DecodeStatus_Malformed);
-
-  if (d->unknown) {
-    if (!UPB_PRIVATE(_upb_Message_AddUnknown)(
-            d->unknown_msg, d->unknown, old_end - d->unknown, &d->arena)) {
-      _upb_FastDecoder_ErrorJmp(d, kUpb_DecodeStatus_OutOfMemory);
-    }
-    d->unknown = new_start;
-  }
-  return new_start;
-}
+UPB_API const char* _upb_Decoder_BufferFlipCallback(upb_EpsCopyInputStream* e,
+                                                    const char* old_end,
+                                                    const char* new_start);
 
 #if UPB_FASTTABLE
 UPB_INLINE
diff --git a/upb/wire/reader.h b/upb/wire/reader.h
index c3ec1a8b1839d..9914837d73113 100644
--- a/upb/wire/reader.h
+++ b/upb/wire/reader.h
@@ -8,8 +8,8 @@
 #ifndef UPB_WIRE_READER_H_
 #define UPB_WIRE_READER_H_
 
+#include "upb/base/internal/endian.h"
 #include "upb/wire/eps_copy_input_stream.h"
-#include "upb/wire/internal/endian.h"
 #include "upb/wire/internal/reader.h"
 #include "upb/wire/types.h"  // IWYU pragma: export
 
@@ -89,7 +89,7 @@ UPB_INLINE const char* upb_WireReader_ReadSize(const char* ptr, int* size) {
 UPB_INLINE const char* upb_WireReader_ReadFixed32(const char* ptr, void* val) {
   uint32_t uval;
   memcpy(&uval, ptr, 4);
-  uval = UPB_PRIVATE(_upb_BigEndian32)(uval);
+  uval = upb_BigEndian32(uval);
   memcpy(val, &uval, 4);
   return ptr + 4;
 }
@@ -102,7 +102,7 @@ UPB_INLINE const char* upb_WireReader_ReadFixed32(const char* ptr, void* val) {
 UPB_INLINE const char* upb_WireReader_ReadFixed64(const char* ptr, void* val) {
   uint64_t uval;
   memcpy(&uval, ptr, 8);
-  uval = UPB_PRIVATE(_upb_BigEndian64)(uval);
+  uval = upb_BigEndian64(uval);
   memcpy(val, &uval, 8);
   return ptr + 8;
 }