diff --git a/pg_wait_sampling.c b/pg_wait_sampling.c
index a35fb94..e165a6a 100644
--- a/pg_wait_sampling.c
+++ b/pg_wait_sampling.c
@@ -76,13 +76,7 @@ static PlannedStmt *pgws_planner_hook(Query *parse,
 									  const char *query_string,
 #endif
 									  int cursorOptions, ParamListInfo boundParams);
-static
-#if PG_VERSION_NUM >= 180000
-bool
-#else
-void
-#endif
-pgws_ExecutorStart(QueryDesc *queryDesc, int eflags);
+static void pgws_ExecutorStart(QueryDesc *queryDesc, int eflags);
 static void pgws_ExecutorRun(QueryDesc *queryDesc,
 							 ScanDirection direction,
 							 uint64 count
@@ -655,6 +649,10 @@ receive_array(SHMRequest request, Size item_size, Size *count)
 	pgws_collector_hdr->request = request;
 	LockRelease(&collectorTag, ExclusiveLock, false);
 
+        /*
+         * Check that the collector was started to avoid NULL
+         * pointer dereference.
+         */
 	if (!pgws_collector_hdr->latch)
 		ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
 						errmsg("pg_wait_sampling collector wasn't started")));
@@ -825,6 +823,14 @@ pg_wait_sampling_reset_profile(PG_FUNCTION_ARGS)
 	pgws_collector_hdr->request = PROFILE_RESET;
 	LockRelease(&collectorTag, ExclusiveLock, false);
 
+        /*
+         * Check that the collector was started to avoid NULL
+         * pointer dereference.
+         */
+	if (!pgws_collector_hdr->latch)
+		ereport(ERROR, (errcode(ERRCODE_INTERNAL_ERROR),
+						errmsg("pg_wait_sampling collector wasn't started")));
+
 	SetLatch(pgws_collector_hdr->latch);
 
 	LockRelease(&queueTag, ExclusiveLock, false);
@@ -982,12 +988,7 @@ pgws_planner_hook(Query *parse,
 /*
  * ExecutorStart hook: save queryId for collector
  */
-static
-#if PG_VERSION_NUM >= 180000
-bool
-#else
-void
-#endif
+static void
 pgws_ExecutorStart(QueryDesc *queryDesc, int eflags)
 {
 	int			i = MyProc - ProcGlobal->allProcs;
@@ -995,9 +996,9 @@ pgws_ExecutorStart(QueryDesc *queryDesc, int eflags)
 	if (pgws_enabled(nesting_level))
 		pgws_proc_queryids[i] = queryDesc->plannedstmt->queryId;
 	if (prev_ExecutorStart)
-		return prev_ExecutorStart(queryDesc, eflags);
+		prev_ExecutorStart(queryDesc, eflags);
 	else
-		return standard_ExecutorStart(queryDesc, eflags);
+		standard_ExecutorStart(queryDesc, eflags);
 }
 
 static void