diff --git a/docs/changes.txt b/docs/changes.txt
index ac8a75c52c..230b970c86 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -591,6 +591,7 @@ All (GUI):
 - Fix updating nested window scrollbars in some cases (sbrowne).
 - Fix wxPGChoices copy ctor (Snoits).
 - Fix wxPixelData<wxImage>::Offset() for alpha (Markus Rollmann).
+- Fix bug in wxImage::ClearAlpha() for shared data (Markus Rollmann).
 
 wxGTK:
 
diff --git a/src/common/image.cpp b/src/common/image.cpp
index b800e58ad8..2120296c56 100644
--- a/src/common/image.cpp
+++ b/src/common/image.cpp
@@ -2040,6 +2040,8 @@ void wxImage::ClearAlpha()
 {
     wxCHECK_RET( HasAlpha(), wxT("image already doesn't have an alpha channel") );
 
+    AllocExclusive();
+
     if ( !M_IMGDATA->m_staticAlpha )
         free( M_IMGDATA->m_alpha );