diff --git a/src/os2/msgdlg.cpp b/src/os2/msgdlg.cpp
index 269d2eebde..8aaa2313cc 100644
--- a/src/os2/msgdlg.cpp
+++ b/src/os2/msgdlg.cpp
@@ -21,6 +21,7 @@
 #include "wx/defs.h"
 #include "wx/utils.h"
 #include "wx/dialog.h"
+#include "wx/app.h"
 #include "wx/msgdlg.h"
 #endif