diff --git a/src/research.h b/src/research.h
index 466a68f..803af5d 100644
--- a/src/research.h
+++ b/src/research.h
@@ -6,4 +6,5 @@ int eliminate_c(void);		// eliminate clusters
 int cascade(void);		// cascade ceiling tiles
 int clear_mat(void);		// clear matched array;
 
+extern int matched;
 #endif