diff --git a/lib/memcpy_kunit.c b/lib/memcpy_kunit.c
index d22fa3838ee9..2b5cc70ac53f 100644
--- a/lib/memcpy_kunit.c
+++ b/lib/memcpy_kunit.c
@@ -272,7 +272,7 @@ static void memset_test(struct kunit *test)
 
 static void strtomem_test(struct kunit *test)
 {
-	static const char input[] = "hi";
+	static const char input[sizeof(unsigned long)] = "hi";
 	static const char truncate[] = "this is too long";
 	struct {
 		unsigned long canary1;