diff --git a/test/api/hb-test.h b/test/api/hb-test.h
index d44e8da41..b866e442a 100644
--- a/test/api/hb-test.h
+++ b/test/api/hb-test.h
@@ -179,8 +179,8 @@ static inline void hb_test_assert_blobs_equal (hb_blob_t *expected_blob, hb_blob
     {
       int expected = *(raw_expected + i);
       int actual = *(raw_actual + i);
-      if (expected != actual) fprintf(stderr, "+%d %02x != %02x\n", i, expected, actual);
-      else fprintf(stderr, "+%d %02x\n", i, expected);
+      if (expected != actual) fprintf(stderr, "+%u %02x != %02x\n", i, expected, actual);
+      else fprintf(stderr, "+%u %02x\n", i, expected);
     }
   }
   g_assert_cmpint(0, ==, memcmp(raw_expected, raw_actual, expected_length));