diff --git a/src/packer.h b/src/packer.h
index 53f29f64..cdf6948d 100644
--- a/src/packer.h
+++ b/src/packer.h
@@ -227,11 +227,13 @@ protected:
     int patchVersion(void *b, int blen);
     void checkPatch(void *b, int blen, int boff, int size);
 
-protected:
     // relocation util
     virtual upx_byte *optimizeReloc32(upx_byte *in,unsigned relocnum,upx_byte *out,upx_byte *image,int bs,int *big);
     virtual unsigned unoptimizeReloc32(upx_byte **in,upx_byte *image,MemBuffer *out,int bs);
 
+    // UI util
+    virtual void updateCallbackSizes(unsigned *, unsigned *) const { }
+
 
 protected:
     InputFile *fi;
diff --git a/src/ui.cpp b/src/ui.cpp
index 8e2d9541..0e7cb832 100644
--- a/src/ui.cpp
+++ b/src/ui.cpp
@@ -356,6 +356,8 @@ void UiPacker::doCallback(unsigned isize, unsigned osize)
     if (s->pass < 0)            // no callback wanted
         return;
 
+    p->updateCallbackSizes(&isize, &osize);
+
     if (s->u_len == 0 || isize > s->u_len)
         return;
     // check if we should update the display