diff --git a/scripts/config.pl b/scripts/config.pl
index 7afc89875..c2be0ba56 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -87,6 +87,7 @@ MBEDTLS_TEST_NULL_ENTROPY
 MBEDTLS_DEPRECATED_REMOVED
 MBEDTLS_HAVE_SSE2
 MBEDTLS_PLATFORM_NO_STD_FUNCTIONS
+MBEDTLS_CTR_DRBG_USE_128_BIT_KEY
 MBEDTLS_ECP_DP_M221_ENABLED
 MBEDTLS_ECP_DP_M383_ENABLED
 MBEDTLS_ECP_DP_M511_ENABLED