diff --git a/runtime/doc/pattern.txt b/runtime/doc/pattern.txt
index 337cbf7..09b4c2c 100644
--- a/runtime/doc/pattern.txt
+++ b/runtime/doc/pattern.txt
@@ -293,6 +293,14 @@
 the "*" is under your right hand middle finger (search to the right and down).
 (this depends on your keyboard layout though).
 
+								*E956*
+In very rare cases a regular expression is used recursively.  This can happen
+when executing a pattern takes a long time and when checkig for messages on
+channels a callback is invoked that also uses a pattern or an autocommand is
+triggered.  In most cases this should be fine, but if a pattern is in use when
+it's used again it fails.  Usually this means there is something wrong with
+the pattern.
+
 ==============================================================================
 2. The definition of a pattern		*search-pattern* *pattern* *[pattern]*
 					*regular-expression* *regexp* *Pattern*