diff --git a/src/SelectedRegion.h b/src/SelectedRegion.h
index d1bc741de..0dcd12441 100644
--- a/src/SelectedRegion.h
+++ b/src/SelectedRegion.h
@@ -30,6 +30,8 @@
 
 #include <wx/defs.h>
 #include <wx/wxchar.h>
+#include <math.h>
+
 class XMLWriter;
 
 class AUDACITY_DLL_API SelectedRegion {