diff --git a/include/mbedtls/md.h b/include/mbedtls/md.h
index 335bc72..490845a 100644
--- a/include/mbedtls/md.h
+++ b/include/mbedtls/md.h
@@ -79,9 +79,8 @@
     /** Digest-specific context */
     void *md_ctx;
 
-    /** HMAC part of the context (WIP: fixed size) */
-    unsigned char ipad[128];
-    unsigned char opad[128];
+    /** HMAC part of the context */
+    void *hmac_ctx;
 } md_context_t;
 
 #define MD_CONTEXT_T_INIT { \