diff --git a/library/chacha20.c b/library/chacha20.c
index 8a3610f..3280629 100644
--- a/library/chacha20.c
+++ b/library/chacha20.c
@@ -148,7 +148,7 @@
     uint32_t working_state[16];
     size_t i;
 
-    memcpy( working_state,
+    mbedtls_platform_memcpy( working_state,
             initial_state,
             CHACHA20_BLOCK_SIZE_BYTES );