diff --git a/docs/shading.html b/docs/shading.html
index 9e3c7218e31..76f25316f86 100644
--- a/docs/shading.html
+++ b/docs/shading.html
@@ -59,6 +59,7 @@ execution.  These are generally used for debugging.
 <li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
     through the color attribute.
 <li><b>useprog</b> - log glUseProgram calls to stderr
+<li><b>errors</b> - GLSL compilation and link errors will be reported to stderr.
 </ul>
 <p>
 Example:  export MESA_GLSL=dump,nopt