diff --git a/src/process-window.c b/src/process-window.c
index de80028..b325599 100644
--- a/src/process-window.c
+++ b/src/process-window.c
@@ -144,7 +144,7 @@ xwininfo_clicked_cb (GtkButton *button, gpointer user_data) {
 	XID id = None;
 
 	Atom atom_NET_WM_PID;
-	long _nitems;
+	unsigned long _nitems;
 	int size;
 	Atom actual_type;
 	int actual_format;