diff --git a/bin/pg_repack.c b/bin/pg_repack.c
index ac3da3e..36ac0b8 100644
--- a/bin/pg_repack.c
+++ b/bin/pg_repack.c
@@ -360,6 +360,11 @@ main(int argc, char *argv[])
 				(errcode(EINVAL),
 				 errmsg("cannot specify --table (-t) and --exclude-extension (-C)")));
 
+		if (exclude_extension_list.head && parent_table_list.head)
+			ereport(ERROR,
+				(errcode(EINVAL),
+				 errmsg("cannot specify --parent-table (-I) and --exclude-extension (-C)")));
+
 		if (noorder)
 			orderby = "";