diff --git a/tests/testimage.h b/tests/testimage.h
index bf14988116..e922e36d63 100644
--- a/tests/testimage.h
+++ b/tests/testimage.h
@@ -62,7 +62,9 @@ public:
                                     "expected 0x%06x",
                                     x, y, *d2, *d1
                                );
-                    break;
+
+                    // Don't show all mismatches, there may be too many of them.
+                    return false;
                 }
 
                 ++d1;
@@ -70,6 +72,10 @@ public:
             }
         }
 
+        // We should never get here as we know that the images are different
+        // and so should have returned from inside the loop above.
+        wxFAIL_MSG("unreachable");
+
         return false;
     }