diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index d4c58e8..5ae0f6b 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -8694,6 +8694,8 @@
 		redraw       disable the redrawing() function
 		char_avail   disable the char_avail() function
 		starting     reset the "starting" variable, see below
+		nfa_fail     makes the NFA regexp engine fail to force a
+			     fallback to the old engine
 		ALL	     clear all overrides ({val} is not used)
 
 		"starting" is to be used when a test should behave like