diff --git a/docs/envvars.html b/docs/envvars.html
index a08f5b94024..08c259cc7b9 100644
--- a/docs/envvars.html
+++ b/docs/envvars.html
@@ -323,6 +323,12 @@ such as the OpenGL program's name and command line arguments.
 <li>See the driver code for other, lesser-used variables.
 </ul>
 
+<h3>WGL environment variables</h3>
+<ul>
+<li>WGL_SWAP_INTERVAL - to set a swap interval, equivalent to calling
+wglSwapIntervalEXT() in an application.  If this environment variable
+is set, application calls to wglSwapIntervalEXT() will have no effect.
+</ul>
 
 <h3>VA-API state tracker environment variables</h3>
 <ul>