diff --git a/src/filters/preg.c b/src/filters/preg.c
index 240078b..d7d2e62 100644
--- a/src/filters/preg.c
+++ b/src/filters/preg.c
@@ -6,6 +6,7 @@
  */
 #include <alloca.h>
 #include <assert.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>