diff --git a/test/default/metamorphic.c b/test/default/metamorphic.c
index 21932fb8..fc883c7f 100644
--- a/test/default/metamorphic.c
+++ b/test/default/metamorphic.c
@@ -36,7 +36,7 @@ mm_generichash(void)
 
         crypto_generichash_init(&st, k, klen, hlen);
         l1 = randombytes_uniform((uint32_t) mlen);
-        l2 = randombytes_uniform((uint32_t) mlen - l1);
+        l2 = randombytes_uniform((uint32_t) (mlen - l1));
         crypto_generichash_update(&st, m, l1);
         crypto_generichash_update(&st, m + l1, l2);
         crypto_generichash_update(&st, m + l1 + l2, mlen - l1 - l2);
@@ -76,7 +76,7 @@ mm_onetimeauth(void)
 
         crypto_onetimeauth_init(&st, k);
         l1 = randombytes_uniform((uint32_t) mlen);
-        l2 = randombytes_uniform((uint32_t) mlen - l1);
+        l2 = randombytes_uniform((uint32_t) (mlen - l1));
         crypto_onetimeauth_update(&st, m, l1);
         crypto_onetimeauth_update(&st, m + l1, l2);
         crypto_onetimeauth_update(&st, m + l1 + l2, mlen - l1 - l2);
@@ -116,7 +116,7 @@ mm_hmacsha256(void)
 
         crypto_auth_hmacsha256_init(&st, k, crypto_auth_hmacsha256_KEYBYTES);
         l1 = randombytes_uniform((uint32_t) mlen);
-        l2 = randombytes_uniform((uint32_t) mlen - l1);
+        l2 = randombytes_uniform((uint32_t) (mlen - l1));
         crypto_auth_hmacsha256_update(&st, m, l1);
         crypto_auth_hmacsha256_update(&st, m + l1, l2);
         crypto_auth_hmacsha256_update(&st, m + l1 + l2, mlen - l1 - l2);
@@ -156,7 +156,7 @@ mm_hmacsha512(void)
 
         crypto_auth_hmacsha512_init(&st, k, crypto_auth_hmacsha512_KEYBYTES);
         l1 = randombytes_uniform((uint32_t) mlen);
-        l2 = randombytes_uniform((uint32_t) mlen - l1);
+        l2 = randombytes_uniform((uint32_t) (mlen - l1));
         crypto_auth_hmacsha512_update(&st, m, l1);
         crypto_auth_hmacsha512_update(&st, m + l1, l2);
         crypto_auth_hmacsha512_update(&st, m + l1 + l2, mlen - l1 - l2);