diff --git a/ext/pgsql/pgsql.c b/ext/pgsql/pgsql.c
index 31ec83cebb2..7c69108ce59 100644
--- a/ext/pgsql/pgsql.c
+++ b/ext/pgsql/pgsql.c
@@ -5472,7 +5472,7 @@ static inline int build_assignment_string(smart_str *querystr, HashTable *ht, co
 				smart_str_append_long(querystr, Z_LVAL_PP(val));
 				break;
 			case IS_DOUBLE:
-				smart_str_appendl(querystr, buf, sprintf(buf, "%f", Z_DVAL_PP(val)));
+				smart_str_appendl(querystr, buf, MIN(snprintf(buf, sizeof(buf), "%f", Z_DVAL_PP(val)), sizeof(buf)-1));
 				break;
 			default:
 				/* should not happen */