diff --git a/src/common/sstream.cpp b/src/common/sstream.cpp
index 3fbbc3fdf3..61f5e8bb99 100644
--- a/src/common/sstream.cpp
+++ b/src/common/sstream.cpp
@@ -28,6 +28,10 @@
 
 #include "wx/sstream.h"
 
+#if wxUSE_UNICODE
+    #include "wx/hashmap.h"
+#endif
+
 // ============================================================================
 // wxStringInputStream implementation
 // ============================================================================