diff --git a/src/msw/gdiimage.cpp b/src/msw/gdiimage.cpp
index 7a26e3036d..d85a3a41c6 100644
--- a/src/msw/gdiimage.cpp
+++ b/src/msw/gdiimage.cpp
@@ -346,6 +346,8 @@ void wxGDIImage::SetScaleFactor(double scale)
 {
     wxCHECK_RET( IsOk(), wxT("invalid bitmap") );
 
+    AllocExclusive();
+
     GetGDIImageData()->m_scaleFactor = scale;
 }