diff --git a/src/gtk/toplevel.cpp b/src/gtk/toplevel.cpp
index f1bf11e450..8123d7a5f8 100644
--- a/src/gtk/toplevel.cpp
+++ b/src/gtk/toplevel.cpp
@@ -43,7 +43,9 @@
     #define HAS_CLIENT_DECOR
 #endif
 #ifdef GDK_WINDOWING_MIR
+    extern "C" {
     #include <gdk/gdkmir.h>
+    }
     #define HAS_CLIENT_DECOR
 #endif
 #ifdef GDK_WINDOWING_BROADWAY