diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 046caec..a566f81 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -500,19 +500,37 @@
     if ( ( ret = mbedtls_md_setup( &md_ctx, md_info, 1 ) ) != 0 )
         goto exit;
 
-    mbedtls_md_hmac_starts( &md_ctx, secret, slen );
-    mbedtls_md_hmac_update( &md_ctx, tmp + md_len, nb );
-    mbedtls_md_hmac_finish( &md_ctx, tmp );
+    ret = mbedtls_md_hmac_starts( &md_ctx, secret, slen );
+    if( ret != 0 )
+        goto exit;
+    ret = mbedtls_md_hmac_update( &md_ctx, tmp + md_len, nb );
+    if( ret != 0 )
+        goto exit;
+    ret = mbedtls_md_hmac_finish( &md_ctx, tmp );
+    if( ret != 0 )
+        goto exit;
 
     for( i = 0; i < dlen; i += md_len )
     {
-        mbedtls_md_hmac_reset ( &md_ctx );
-        mbedtls_md_hmac_update( &md_ctx, tmp, md_len + nb );
-        mbedtls_md_hmac_finish( &md_ctx, h_i );
+        ret = mbedtls_md_hmac_reset ( &md_ctx );
+        if( ret != 0 )
+            goto exit;
+        ret = mbedtls_md_hmac_update( &md_ctx, tmp, md_len + nb );
+        if( ret != 0 )
+            goto exit;
+        ret = mbedtls_md_hmac_finish( &md_ctx, h_i );
+        if( ret != 0 )
+            goto exit;
 
-        mbedtls_md_hmac_reset ( &md_ctx );
-        mbedtls_md_hmac_update( &md_ctx, tmp, md_len );
-        mbedtls_md_hmac_finish( &md_ctx, tmp );
+        ret = mbedtls_md_hmac_reset ( &md_ctx );
+        if( ret != 0 )
+            goto exit;
+        ret = mbedtls_md_hmac_update( &md_ctx, tmp, md_len );
+        if( ret != 0 )
+            goto exit;
+        ret = mbedtls_md_hmac_finish( &md_ctx, tmp );
+        if( ret != 0 )
+            goto exit;
 
         k = ( i + md_len > dlen ) ? dlen % md_len : md_len;
 
@@ -958,8 +976,12 @@
        For AEAD-based ciphersuites, there is nothing to do here. */
     if( mac_key_len != 0 )
     {
-        mbedtls_md_hmac_starts( &transform->md_ctx_enc, mac_enc, mac_key_len );
-        mbedtls_md_hmac_starts( &transform->md_ctx_dec, mac_dec, mac_key_len );
+        ret = mbedtls_md_hmac_starts( &transform->md_ctx_enc, mac_enc, mac_key_len );
+        if( ret != 0 )
+            goto end;
+        ret = mbedtls_md_hmac_starts( &transform->md_ctx_dec, mac_dec, mac_key_len );
+        if( ret != 0 )
+            goto end;
     }
 #endif
 #endif /* MBEDTLS_SSL_SOME_SUITES_USE_MAC */