diff --git a/docs/cmdline-opts/_ENVIRONMENT.md b/docs/cmdline-opts/_ENVIRONMENT.md
index 1ac85fb128..a3c13ae0c0 100644
--- a/docs/cmdline-opts/_ENVIRONMENT.md
+++ b/docs/cmdline-opts/_ENVIRONMENT.md
@@ -3,7 +3,8 @@
 # ENVIRONMENT
 The environment variables can be specified in lower case or upper case. The
 lower case version has precedence. `http_proxy` is an exception as it is only
-available in lower case.
+available in lower case. (Note that some systems, like Windows, do not
+differentiate between environment variables using different case.)
 
 Using an environment variable to set the proxy has the same effect as using
 the --proxy option.
diff --git a/docs/libcurl/libcurl-env.md b/docs/libcurl/libcurl-env.md
index 6ef11ac9a3..5ce846df8a 100644
--- a/docs/libcurl/libcurl-env.md
+++ b/docs/libcurl/libcurl-env.md
@@ -32,8 +32,8 @@ uses the **ftp_proxy** variable.
 
 These proxy variables are also checked for in their uppercase versions, except
 the **http_proxy** one which is only used lowercase. Note also that some
-systems actually have a case insensitive handling of environment variables and
-then of course **HTTP_PROXY** still works.
+systems (like Windows) have a case insensitive handling of environment
+variables and then of course **HTTP_PROXY** still works.
 
 An exception exists for the WebSocket **ws** and **wss** URL schemes, where
 libcurl first checks **ws_proxy** or **wss_proxy** but if they are not set, it