diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index accf51e..7f403c1 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -886,6 +886,10 @@
 #error "MBEDTLS_SSL_DTLS_SRTP defined, but not all prerequisites"
 #endif
 
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH) && ( !defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH) )
+#error "MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH defined, but not all prerequisites"
+#endif
+
 /*
  * Avoid warning from -pedantic. This is a convenient place for this
  * workaround since this is included by every single file before the
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index c5f65e1..818dc0c 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1980,6 +1980,8 @@
  * \def MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
  *
  * Enable modifying the maximum I/O buffer size.
+ *
+ * Requires: MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
  */
 //#define MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH