diff --git a/runtime/doc/testing.txt b/runtime/doc/testing.txt
index 1252ce3..6998a6e 100644
--- a/runtime/doc/testing.txt
+++ b/runtime/doc/testing.txt
@@ -268,6 +268,9 @@
 		Current supported values for {name} are:
 
 		{name}	     effect when {val} is non-zero ~
+		alloc_lines  make a copy of every buffer line into allocated
+			     memory, so that memory access errors can be found
+			     by valgrind
 		autoload     `import autoload` will load the script right
 			     away, not postponed until an item is used
 		char_avail   disable the char_avail() function
@@ -287,7 +290,8 @@
 		uptime 	     overrules sysinfo.uptime
 		vterm_title  setting the window title by a job running in a
 			     terminal window
-		ALL	     clear all overrides ({val} is not used)
+		ALL	     clear all overrides, except alloc_lines ({val} is
+			     not used)
 
 		"starting" is to be used when a test should behave like
 		startup was done.  Since the tests are run by sourcing a