diff --git a/vncviewer/UserDialog.cxx b/vncviewer/UserDialog.cxx
index 0c2559f..f36d843 100644
--- a/vncviewer/UserDialog.cxx
+++ b/vncviewer/UserDialog.cxx
@@ -16,6 +16,10 @@
  * USA.
  */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include <assert.h>
 #include <stdio.h>
 #include <string.h>