diff --git a/src/util/pactree.c b/src/util/pactree.c
index b8832912..11ca4b9e 100644
--- a/src/util/pactree.c
+++ b/src/util/pactree.c
@@ -19,6 +19,7 @@
 
 #include "config.h"
 
+#include <ctype.h>
 #include <getopt.h>
 #include <stdio.h>
 #include <string.h>