diff --git a/src/pattern.c b/src/pattern.c
index d667cef..ce60f76 100644
--- a/src/pattern.c
+++ b/src/pattern.c
@@ -1117,7 +1117,7 @@
 	struct pat_idx_elt *elt;
 	const char *args[2];
 	int opaque = 0;
-	unsigned int mask;
+	unsigned int mask = 0;
 
 	/* no real pattern */
 	if (!expr->match || expr->match == pat_match_nothing)