diff --git a/pc/externalhmac.cc b/pc/externalhmac.cc
index 348b33b45d..0e82fffc28 100644
--- a/pc/externalhmac.cc
+++ b/pc/externalhmac.cc
@@ -51,10 +51,10 @@ static const char kExternalHmacDescription[] =
 static const srtp_auth_type_t external_hmac  = {
   external_hmac_alloc,
   external_hmac_dealloc,
-  (srtp_auth_init_func)    external_hmac_init,
-  (srtp_auth_compute_func) external_hmac_compute,
-  (srtp_auth_update_func)  external_hmac_update,
-  (srtp_auth_start_func)   external_hmac_start,
+  external_hmac_init,
+  external_hmac_compute,
+  external_hmac_update,
+  external_hmac_start,
   const_cast<char*>(kExternalHmacDescription),
   const_cast<srtp_auth_test_case_t*>(&kExternalHmacTestCase0),
   EXTERNAL_HMAC_SHA1
@@ -104,33 +104,34 @@ srtp_err_status_t external_hmac_dealloc(srtp_auth_t* a) {
   return srtp_err_status_ok;
 }
 
-srtp_err_status_t external_hmac_init(ExternalHmacContext* state,
+srtp_err_status_t external_hmac_init(void* state,
                                      const uint8_t* key,
                                      int key_len) {
   if (key_len > HMAC_KEY_LENGTH)
     return srtp_err_status_bad_param;
 
-  memset(state->key, 0, key_len);
-  memcpy(state->key, key, key_len);
-  state->key_length = key_len;
+  ExternalHmacContext* context = static_cast<ExternalHmacContext*>(state);
+  memset(context->key, 0, key_len);
+  memcpy(context->key, key, key_len);
+  context->key_length = key_len;
   return srtp_err_status_ok;
 }
 
-srtp_err_status_t external_hmac_start(ExternalHmacContext* state) {
+srtp_err_status_t external_hmac_start(void* /*state*/) {
   return srtp_err_status_ok;
 }
 
-srtp_err_status_t external_hmac_update(ExternalHmacContext* state,
-                                       const uint8_t* message,
-                                       int msg_octets) {
+srtp_err_status_t external_hmac_update(void* /*state*/,
+                                       const uint8_t* /*message*/,
+                                       int /*msg_octets*/) {
   return srtp_err_status_ok;
 }
 
-srtp_err_status_t external_hmac_compute(ExternalHmacContext* state,
-                                       const void* message,
-                                       int msg_octets,
-                                       int tag_len,
-                                       uint8_t* result) {
+srtp_err_status_t external_hmac_compute(void* /*state*/,
+                                        const uint8_t* /*message*/,
+                                        int /*msg_octets*/,
+                                        int tag_len,
+                                        uint8_t* result) {
   memcpy(result, kExternalHmacFakeTag, tag_len);
   return srtp_err_status_ok;
 }
diff --git a/pc/externalhmac.h b/pc/externalhmac.h
index 7fb9f25fbf..187496c7cd 100644
--- a/pc/externalhmac.h
+++ b/pc/externalhmac.h
@@ -49,18 +49,18 @@ srtp_err_status_t external_hmac_alloc(srtp_auth_t** a,
 
 srtp_err_status_t external_hmac_dealloc(srtp_auth_t* a);
 
-srtp_err_status_t external_hmac_init(ExternalHmacContext* state,
+srtp_err_status_t external_hmac_init(void* state,
                                      const uint8_t* key,
                                      int key_len);
 
-srtp_err_status_t external_hmac_start(ExternalHmacContext* state);
+srtp_err_status_t external_hmac_start(void* state);
 
-srtp_err_status_t external_hmac_update(ExternalHmacContext* state,
+srtp_err_status_t external_hmac_update(void* state,
                                        const uint8_t* message,
                                        int msg_octets);
 
-srtp_err_status_t external_hmac_compute(ExternalHmacContext* state,
-                                        const void* message,
+srtp_err_status_t external_hmac_compute(void* state,
+                                        const uint8_t* message,
                                         int msg_octets,
                                         int tag_len,
                                         uint8_t* result);