diff --git a/test/test_ecdh.c b/test/test_ecdh.c
index 2388126..92d9374 100644
--- a/test/test_ecdh.c
+++ b/test/test_ecdh.c
@@ -19,6 +19,7 @@ int fake_rng(uint8_t *dest, unsigned size) {
 
         unsigned amount = (size > 8 ? 8 : size);
         memcpy(dest, &g_rand, amount);
+        dest += amount;
         size -= amount;
     }
     return 1;
diff --git a/test/test_ecdsa.c b/test/test_ecdsa.c
index 2fc75be..0c6f0e2 100644
--- a/test/test_ecdsa.c
+++ b/test/test_ecdsa.c
@@ -19,6 +19,7 @@ int fake_rng(uint8_t *dest, unsigned size) {
 
         unsigned amount = (size > 8 ? 8 : size);
         memcpy(dest, &g_rand, amount);
+        dest += amount;
         size -= amount;
     }
     return 1;
diff --git a/test/test_ecdsa_deterministic.c b/test/test_ecdsa_deterministic.c
index 243f164..77d79aa 100644
--- a/test/test_ecdsa_deterministic.c
+++ b/test/test_ecdsa_deterministic.c
@@ -19,6 +19,7 @@ int fake_rng(uint8_t *dest, unsigned size) {
 
         unsigned amount = (size > 8 ? 8 : size);
         memcpy(dest, &g_rand, amount);
+        dest += amount;
         size -= amount;
     }
     return 1;