diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 6332d148f..ba4a60815 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -238,7 +238,7 @@
    implicit sequence number. */
 #define MBEDTLS_SSL_HEADER_LEN 13
 
-#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+#if !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 #define MBEDTLS_SSL_IN_BUFFER_LEN  \
     ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_IN_PAYLOAD_LEN ) )
 #else
@@ -247,7 +247,7 @@
       + ( MBEDTLS_SSL_CID_IN_LEN_MAX ) )
 #endif
 
-#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+#if !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 #define MBEDTLS_SSL_OUT_BUFFER_LEN  \
     ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_OUT_PAYLOAD_LEN ) )
 #else