diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 68e8d04..006b255 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -620,6 +620,7 @@
 
 /* Dummy type used only for its size */
 union mbedtls_ssl_premaster_secret {
+    unsigned char dummy; /* Make the union non-empty even with SSL disabled */
 #if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
     unsigned char _pms_rsa[48];                         /* RFC 5246 8.1.1 */
 #endif