diff --git a/tests/include/test/ssl_helpers.h b/tests/include/test/ssl_helpers.h
index 281d1f5..2c6bf79 100644
--- a/tests/include/test/ssl_helpers.h
+++ b/tests/include/test/ssl_helpers.h
@@ -101,6 +101,9 @@
 #endif
 } mbedtls_test_handshake_test_options;
 
+/*
+ * Buffer structure for custom I/O callbacks.
+ */
 typedef struct mbedtls_test_ssl_buffer {
     size_t start;
     size_t content_length;
@@ -460,6 +463,12 @@
         }                                       \
     } while (0)
 
+#if MBEDTLS_SSL_CID_OUT_LEN_MAX > MBEDTLS_SSL_CID_IN_LEN_MAX
+#define SSL_CID_LEN_MIN MBEDTLS_SSL_CID_IN_LEN_MAX
+#else
+#define SSL_CID_LEN_MIN MBEDTLS_SSL_CID_OUT_LEN_MAX
+#endif
+
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
     defined(MBEDTLS_CIPHER_MODE_CBC) && defined(MBEDTLS_AES_C)
 int mbedtls_test_psa_cipher_encrypt_helper(mbedtls_ssl_transform *transform,