diff --git a/doc/Slime.htm b/doc/Slime.htm
index 79f6bec..bb4b2e2 100644
--- a/doc/Slime.htm
+++ b/doc/Slime.htm
@@ -10,6 +10,7 @@
   <h2>Slime</h2>
   <p>Requires <b>ECL threads</b>.</p>
   <p>This should work with any Slime version that plays together with ECL.</p>
+  <p><i><b>Warning:</b> I experienced occasional freezing of Emacs/Slime using Slime version <b>v2.20</b>; so, if you have trouble, please switch back to an earlier version (it's also recommended to purge your <code>~/.slime</code> directory, if present).</i></p>
   <br>
   <h3>Prepare</h3>
   <ul>