diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2d869882fe..0a81ef41e1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -778,6 +778,9 @@ if(CURL_USE_OPENSSL)
     set(_openssl "AmiSSL")
   else()
     set(_openssl "OpenSSL")
+    if(OPENSSL_VERSION VERSION_LESS 1.1.1)
+      message(WARNING "OpenSSL ${OPENSSL_VERSION} does not support TLS 1.3.")
+    endif()
   endif()
 endif()