diff --git a/meta-phosphor/classes/image_types_phosphor.bbclass b/meta-phosphor/classes/image_types_phosphor.bbclass
index 6612bd6..8242c78 100644
--- a/meta-phosphor/classes/image_types_phosphor.bbclass
+++ b/meta-phosphor/classes/image_types_phosphor.bbclass
@@ -281,7 +281,7 @@
         bb.debug(1, 'Spanning start=' + str(start_kb) + 'K end=' + str(finish_kb) + 'K')
         bb.debug(1, 'Compare needed=' + str(imgsize) + ' available=' + str(maxsize) + ' margin=' + str(maxsize - imgsize))
         if imgsize > maxsize:
-            bb.fatal("Image '%s' is too large!" % imgpath)
+            bb.fatal("Image '%s' is %d bytes too large!" % (imgpath, imgsize - maxsize))
 
         subprocess.check_call(['dd', 'bs=1k', 'conv=notrunc',
                                'seek=%d' % start_kb,