diff --git a/vncviewer/Viewport.cxx b/vncviewer/Viewport.cxx
index 0936a63..72de8e8 100644
--- a/vncviewer/Viewport.cxx
+++ b/vncviewer/Viewport.cxx
@@ -17,6 +17,10 @@
  * USA.
  */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include <assert.h>
 #include <stdio.h>
 #include <string.h>