diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index c4adbf98fac7..45c0cb992218 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -407,7 +407,7 @@ static int dmirror_fault(struct dmirror *dmirror, unsigned long start,
 
 	/* Since the mm is for the mirrored process, get a reference first. */
 	if (!mmget_not_zero(mm))
-		return 0;
+		return -EFAULT;
 
 	for (addr = start; addr < end; addr = range.end) {
 		range.start = addr;