diff --git a/reftable/record.c b/reftable/record.c
index 23b497adab..5506f3e913 100644
--- a/reftable/record.c
+++ b/reftable/record.c
@@ -159,6 +159,30 @@ int reftable_encode_key(int *restart, struct string_view dest,
 	return start.len - dest.len;
 }
 
+int reftable_decode_keylen(struct string_view in,
+			   uint64_t *prefix_len,
+			   uint64_t *suffix_len,
+			   uint8_t *extra)
+{
+	size_t start_len = in.len;
+	int n;
+
+	n = get_var_int(prefix_len, &in);
+	if (n < 0)
+		return -1;
+	string_view_consume(&in, n);
+
+	n = get_var_int(suffix_len, &in);
+	if (n <= 0)
+		return -1;
+	string_view_consume(&in, n);
+
+	*extra = (uint8_t)(*suffix_len & 0x7);
+	*suffix_len >>= 3;
+
+	return start_len - in.len;
+}
+
 int reftable_decode_key(struct strbuf *last_key, uint8_t *extra,
 			struct string_view in)
 {
@@ -167,19 +191,11 @@ int reftable_decode_key(struct strbuf *last_key, uint8_t *extra,
 	uint64_t suffix_len = 0;
 	int n;
 
-	n = get_var_int(&prefix_len, &in);
+	n = reftable_decode_keylen(in, &prefix_len, &suffix_len, extra);
 	if (n < 0)
 		return -1;
 	string_view_consume(&in, n);
 
-	n = get_var_int(&suffix_len, &in);
-	if (n <= 0)
-		return -1;
-	string_view_consume(&in, n);
-
-	*extra = (uint8_t)(suffix_len & 0x7);
-	suffix_len >>= 3;
-
 	if (in.len < suffix_len ||
 	    prefix_len > last_key->len)
 		return -1;
diff --git a/reftable/record.h b/reftable/record.h
index 826ee1c55c..d778133e6e 100644
--- a/reftable/record.h
+++ b/reftable/record.h
@@ -86,6 +86,12 @@ int reftable_encode_key(int *is_restart, struct string_view dest,
 			struct strbuf prev_key, struct strbuf key,
 			uint8_t extra);
 
+/* Decode a record's key lengths. */
+int reftable_decode_keylen(struct string_view in,
+			   uint64_t *prefix_len,
+			   uint64_t *suffix_len,
+			   uint8_t *extra);
+
 /*
  * Decode into `last_key` and `extra` from `in`. `last_key` is expected to
  * contain the decoded key of the preceding record, if any.