diff --git a/src/backend/storage/ipc/ipc.c b/src/backend/storage/ipc/ipc.c
index 6bc0b06..bfc7764 100644
--- a/src/backend/storage/ipc/ipc.c
+++ b/src/backend/storage/ipc/ipc.c
@@ -291,10 +291,12 @@ atexit_callback(void)
 void
 on_proc_exit(pg_on_exit_callback function, Datum arg)
 {
-	if (on_proc_exit_index >= MAX_ON_EXITS)
-		ereport(FATAL,
-				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-				 errmsg_internal("out of on_proc_exit slots")));
+	int 	i;
+	
+	/* check no duplicates and there are rooms */
+	for (i = 0; i < on_proc_exit_index; i++)
+		Assert (on_proc_exit_list[i] != function);
+	Assert (on_proc_exit_index < MAX_ON_EXITS);
 
 	on_proc_exit_list[on_proc_exit_index].function = function;
 	on_proc_exit_list[on_proc_exit_index].arg = arg;
@@ -319,10 +321,12 @@ on_proc_exit(pg_on_exit_callback function, Datum arg)
 void
 before_shmem_exit(pg_on_exit_callback function, Datum arg)
 {
-	if (before_shmem_exit_index >= MAX_ON_EXITS)
-		ereport(FATAL,
-				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-				 errmsg_internal("out of before_shmem_exit slots")));
+	int		i;
+	
+	/* check no duplicated callbacks and there are rooms */
+	for (i = 0; i < before_shmem_exit_index; i++)
+		Assert (before_shmem_exit_list[i] != function);
+	Assert (before_shmem_exit_index < MAX_ON_EXITS);
 
 	before_shmem_exit_list[before_shmem_exit_index].function = function;
 	before_shmem_exit_list[before_shmem_exit_index].arg = arg;
@@ -347,10 +351,12 @@ before_shmem_exit(pg_on_exit_callback function, Datum arg)
 void
 on_shmem_exit(pg_on_exit_callback function, Datum arg)
 {
-	if (on_shmem_exit_index >= MAX_ON_EXITS)
-		ereport(FATAL,
-				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-				 errmsg_internal("out of on_shmem_exit slots")));
+	int 	i;
+	
+	/* check no duplicates and there are rooms */
+	for (i = 0; i < on_shmem_exit_index; i++)
+		Assert (on_shmem_exit_list[i] != function);
+	Assert (on_shmem_exit_index < MAX_ON_EXITS);
 
 	on_shmem_exit_list[on_shmem_exit_index].function = function;
 	on_shmem_exit_list[on_shmem_exit_index].arg = arg;