diff --git a/src/p_tags.h b/src/p_tags.h
index 75d397d8d..c3162d9b5 100644
--- a/src/p_tags.h
+++ b/src/p_tags.h
@@ -49,6 +49,7 @@ public:
 		startForSector.Clear();
 		startForLine.Clear();
 		memset(TagHashFirst, -1, sizeof(TagHashFirst));
+		memset(IDHashFirst, -1, sizeof(IDHashFirst));
 	}
 
 	bool SectorHasTags(const sector_t *sector) const;