diff --git a/scripts/ecc-heap.sh b/scripts/ecc-heap.sh
index 8d1beee5f..71c33f855 100755
--- a/scripts/ecc-heap.sh
+++ b/scripts/ecc-heap.sh
@@ -54,6 +54,7 @@ cat << EOF >$CONFIG_H
 
 #define MBEDTLS_BIGNUM_C
 #define MBEDTLS_ECP_C
+#define MBEDTLS_ECP_NO_INTERNAL_RNG
 #define MBEDTLS_ASN1_PARSE_C
 #define MBEDTLS_ASN1_WRITE_C
 #define MBEDTLS_ECDSA_C