diff --git a/contrib/hstore/hstore_gist.c b/contrib/hstore/hstore_gist.c
index 3df00493e8..fe343739eb 100644
--- a/contrib/hstore/hstore_gist.c
+++ b/contrib/hstore/hstore_gist.c
@@ -77,7 +77,7 @@ typedef struct
 
 /* shorthand for calculating CRC-32 of a single chunk of data. */
 static pg_crc32
-crc32_sz(char *buf, int size)
+crc32_sz(const char *buf, int size)
 {
 	pg_crc32	crc;