diff --git a/xcape.c b/xcape.c
index c1ca0d3..329c25e 100644
--- a/xcape.c
+++ b/xcape.c
@@ -128,6 +128,11 @@ int main (int argc, char **argv)
     self->data_conn = XOpenDisplay (NULL);
     self->ctrl_conn = XOpenDisplay (NULL);
 
+    if (!self->data_conn || !self->ctrl_conn)
+    {
+        fprintf (stderr, "Unable to connect to X11 display. Is $DISPLAY set?\sn");
+        exit (EXIT_FAILURE);
+    }
     if (!XQueryExtension (self->ctrl_conn,
                 "XTEST", &dummy, &dummy, &dummy))
     {