--- a/src/hll.c
+++ b/src/hll.c
@@ -127,7 +127,7 @@ enum {
 static Oid hllAggregateArray[HLL_AGGREGATE_COUNT];
 static bool aggregateValuesInitialized = false;
 
-bool ForceGroupAgg = false;
+static bool ForceGroupAgg = false;
 
 static create_upper_paths_hook_type previous_upper_path_hook;
 static void RegisterConfigVariables(void);
