diff --git a/include/test/test.h b/include/test/test.h
index 1369963..755baf8 100644
--- a/include/test/test.h
+++ b/include/test/test.h
@@ -942,7 +942,7 @@
 			      "Asserted " #ptr " is not null, but is.");       \
 	if (IS_ERR(__ptr))						       \
 		__stream->add(__stream,					       \
-			      "Asserted " #ptr " is not error, but is: %ld",   \
+			      "Asserted " #ptr " is not error, but is: %s",   \
 			      strerror_r(-PTR_ERR(__ptr), buf, sizeof(buf)));  \
 									       \
 	ASSERT_END(test, !IS_ERR_OR_NULL(__ptr), __stream);		       \