diff --git a/library/cmac.c b/library/cmac.c
index b2fe713..5575d5c 100644
--- a/library/cmac.c
+++ b/library/cmac.c
@@ -65,6 +65,8 @@
 #endif /* MBEDTLS_SELF_TEST */
 #endif /* MBEDTLS_PLATFORM_C */
 
+#if !defined(MBEDTLS_CMAC_ALT)
+
 /* Implementation that should never be optimized out by the compiler */
 static void mbedtls_zeroize( void *v, size_t n ) {
     volatile unsigned char *p = (unsigned char*)v; while( n-- ) *p++ = 0;
@@ -468,6 +470,8 @@
 }
 #endif /* MBEDTLS_AES_C */
 
+#endif /* !MBEDTLS_CMAC_ALT */
+
 #if defined(MBEDTLS_SELF_TEST)
 /*
  * CMAC test data for SP800-38B