diff --git a/contrib/ltree/_ltree_gist.c b/contrib/ltree/_ltree_gist.c
index c4623ec020f02bf657ced33233ed520f435118d7..359ddfe4d7d0cbe80b2c12adb5f1250b8748d097 100644
--- a/contrib/ltree/_ltree_gist.c
+++ b/contrib/ltree/_ltree_gist.c
@@ -85,7 +85,7 @@ _ltree_compress(PG_FUNCTION_ARGS)
 		key->len = len;
 		key->flag = 0;
 
-		MemSet(LTG_SIGN(key), 0, sizeof(ASIGLEN));
+		MemSet(LTG_SIGN(key), 0, ASIGLEN);
 		while (num > 0)
 		{
 			hashing(LTG_SIGN(key), item);