diff --git a/include/drivers/auth/mbedtls/mbedtls_config.h b/include/drivers/auth/mbedtls/mbedtls_config.h
index f8f2608..59aeea9 100644
--- a/include/drivers/auth/mbedtls/mbedtls_config.h
+++ b/include/drivers/auth/mbedtls/mbedtls_config.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -95,4 +95,16 @@
 #include "mbedtls/check_config.h"
 #endif
 
+/*
+ * Determine Mbed TLS heap size
+ * 13312 = 13*1024
+ * 7168 = 7*1024
+ */
+#if (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA) \
+	|| (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA)
+#define TF_MBEDTLS_HEAP_SIZE		U(13312)
+#elif (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA)
+#define TF_MBEDTLS_HEAP_SIZE		U(7168)
+#endif
+
 #endif /* __MBEDTLS_CONFIG_H__ */