diff --git a/src/common/imagbmp.cpp b/src/common/imagbmp.cpp
index c478f0ccff..7bc9bee950 100644
--- a/src/common/imagbmp.cpp
+++ b/src/common/imagbmp.cpp
@@ -1162,7 +1162,7 @@ bool wxBMPHandler::LoadDib(wxImage *image, wxInputStream& stream,
         //
         // Note: hardcode its size as struct BITMAPINFOHEADER is not defined on
         // non-MSW platforms.
-        const size_t sizeBITMAPINFOHEADER = 40;
+        const wxInt32 sizeBITMAPINFOHEADER = 40;
         if ( hdrSize > sizeBITMAPINFOHEADER )
         {
             if ( stream.SeekI(hdrSize - sizeBITMAPINFOHEADER, wxFromCurrent) == wxInvalidOffset )