diff --git a/test/lib/testing.c b/test/lib/testing.c
index f787f875..5d2437f4 100644
--- a/test/lib/testing.c
+++ b/test/lib/testing.c
@@ -201,7 +201,7 @@ void testingprivTLogvfFull(testingT *t, const char *file, long line, const char
 {
 	// TODO extract filename from file
 	testingprivOutbufPrintf(t->outbuf, "%s:%ld: ", file, line);
-	testingprivOutbufPrintf(t->outbuf, format, ap);
+	testingprivOutbufVprintf(t->outbuf, format, ap);
 	testingprivOutbufPrintf(t->outbuf, "\n");
 }