diff --git a/src/core/meshcop/dtls.cpp b/src/core/meshcop/dtls.cpp
index ab77c108f..080783ac5 100644
--- a/src/core/meshcop/dtls.cpp
+++ b/src/core/meshcop/dtls.cpp
@@ -295,6 +295,8 @@ otError Dtls::Setup(bool aClient)
     mbedtls_ssl_conf_rng(&mConf, mbedtls_ctr_drbg_random, Random::Crypto::MbedTlsContextGet());
     mbedtls_ssl_conf_min_version(&mConf, MBEDTLS_SSL_MAJOR_VERSION_3, MBEDTLS_SSL_MINOR_VERSION_3);
     mbedtls_ssl_conf_max_version(&mConf, MBEDTLS_SSL_MAJOR_VERSION_3, MBEDTLS_SSL_MINOR_VERSION_3);
+
+    assert(mCipherSuites[1] == 0);
     mbedtls_ssl_conf_ciphersuites(&mConf, mCipherSuites);
     mbedtls_ssl_conf_export_keys_cb(&mConf, HandleMbedtlsExportKeys, this);
     mbedtls_ssl_conf_handshake_timeout(&mConf, 8000, 60000);
@@ -364,8 +366,6 @@ int Dtls::SetApplicationCoapSecureKeys(void)
 {
     int rval = 0;
 
-    VerifyOrExit(&mCipherSuites[0] != NULL, rval = MBEDTLS_ERR_SSL_BAD_INPUT_DATA);
-
     switch (mCipherSuites[0])
     {
     case MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8: