diff --git a/scripts/ecc-heap.sh b/scripts/ecc-heap.sh
index 8d1beee..71c33f8 100755
--- a/scripts/ecc-heap.sh
+++ b/scripts/ecc-heap.sh
@@ -54,6 +54,7 @@
 
 #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