diff --git a/tests/pb/test_decoder.cc b/tests/pb/test_decoder.cc
index 94293cb8c5..a01e9999ed 100644
--- a/tests/pb/test_decoder.cc
+++ b/tests/pb/test_decoder.cc
@@ -570,15 +570,14 @@ uint32_t Hash(const string& proto, const string* expected_output, size_t seam1,
 }
 
 void CheckBytesParsed(const upb::pb::Decoder& decoder, size_t ofs) {
-  // We could have parsed as many as 10 bytes fewer than what the decoder
-  // previously accepted, since we can buffer up to 12 partial bytes internally
-  // before accumulating an entire value.
-  const int MAX_BUFFERED = 14;
-
   // We can't have parsed more data than the decoder callback is telling us it
   // parsed.
   ASSERT(decoder.BytesParsed() <= ofs);
-  ASSERT(ofs <= (decoder.BytesParsed() + MAX_BUFFERED));
+
+  // The difference between what we've decoded and what the decoder has accepted
+  // represents the internally buffered amount.  This amount should not exceed
+  // this value which comes from decoder.int.h.
+  ASSERT(ofs <= (decoder.BytesParsed() + UPB_DECODER_MAX_RESIDUAL_BYTES));
 }
 
 static bool parse(VerboseParserEnvironment* env,
diff --git a/upb/pb/decoder.h b/upb/pb/decoder.h
index 65316b4e40..8172a9971e 100644
--- a/upb/pb/decoder.h
+++ b/upb/pb/decoder.h
@@ -36,6 +36,13 @@ UPB_DECLARE_TYPE(upb::pb::DecoderMethodOptions, upb_pbdecodermethodopts)
 UPB_DECLARE_DERIVED_TYPE(upb::pb::DecoderMethod, upb::RefCounted,
                          upb_pbdecodermethod, upb_refcounted)
 
+/* The maximum number of bytes we are required to buffer internally between
+ * calls to the decoder.  The value is 14: a 5 byte unknown tag plus ten-byte
+ * varint, less one because we are buffering an incomplete value.
+ *
+ * Should only be used by unit tests. */
+#define UPB_DECODER_MAX_RESIDUAL_BYTES 14
+
 #ifdef __cplusplus
 
 /* The parameters one uses to construct a DecoderMethod.
diff --git a/upb/pb/decoder.int.h b/upb/pb/decoder.int.h
index b7e462b547..f2bf242bb8 100644
--- a/upb/pb/decoder.int.h
+++ b/upb/pb/decoder.int.h
@@ -218,11 +218,8 @@ struct upb_pbdecoder {
   /* Overall stream offset of "buf." */
   uint64_t bufstart_ofs;
 
-  /* Buffer for residual bytes not parsed from the previous buffer.
-   * The maximum number of residual bytes we require is 12; a five-byte
-   * unknown tag plus a ten-byte value, less one because the value
-   * is only a partial value. */
-  char residual[14];
+  /* Buffer for residual bytes not parsed from the previous buffer. */
+  char residual[UPB_DECODER_MAX_RESIDUAL_BYTES];
   char *residual_end;
 
   /* Bytes of data that should be discarded from the input beore we start