diff --git a/lslopt/lslfoldconst.py b/lslopt/lslfoldconst.py
index 7c98bac..79ea3d8 100644
--- a/lslopt/lslfoldconst.py
+++ b/lslopt/lslfoldconst.py
@@ -1001,7 +1001,7 @@ class foldconst(object):
                                 warning(u"Can't optimize call to %s because it would generate a tab character (you can force the optimization with the 'foldtabs' option, or disable this warning by disabling the 'warntabs' option)." % node['name'].decode('utf8'))
                             return
                     parent[index] = {'nt':'CONST', 't':node['t'], 'value':value, 'SEF':True}
-                elif node['name'] == 'llGetListLength':
+                elif self.optlistlength and node['name'] == 'llGetListLength':
                     # Convert llGetListLength(expr) to (expr != [])
                     node = {'nt':'CONST', 't':'list', 'value':[]}
                     parent[index] = node = {'nt':'!=', 't':'list', 'ch':[child[0], node]}
diff --git a/lslopt/lsloptimizer.py b/lslopt/lsloptimizer.py
index 27b0ee6..3684360 100644
--- a/lslopt/lsloptimizer.py
+++ b/lslopt/lsloptimizer.py
@@ -74,6 +74,7 @@ class optimizer(foldconst, renamer, deadcode):
         self.shrinknames = 'shrinknames' in options
 
         self.constfold = 'constfold' in options
+        self.optlistlength = 'listlength' in options
         self.dcr = 'dcr' in options
 
         # Math that works fine except in rare corner-cases can be optimized.
diff --git a/main.py b/main.py
index 25f2533..2884afd 100755
--- a/main.py
+++ b/main.py
@@ -282,6 +282,7 @@ Case insensitive.
                        would keep a single copy of "longstring", while if the
                        strings are added, both "alongstring" and "blongstring"
                        take memory.
+  ListLength         + Optimize llGetListLength(arg) to arg!=[].
 
   Miscellaneous options
 
@@ -318,7 +319,7 @@ validoptions = frozenset(('extendedglobalexpr','breakcont','extendedtypecast',
     'extendedassignment','allowkeyconcat','allowmultistrings','duplabels',
     'lazylists','enableswitch','errmissingdefault','funcoverride','optimize',
     'optsigns','optfloats','constfold','dcr','shrinknames','addstrings',
-    'foldtabs','warntabs','processpre','explicitcast',
+    'foldtabs','warntabs','processpre','explicitcast','listlength',
     'help','lso','expr'
     # 'clear' is handled as a special case
 ))
@@ -334,6 +335,7 @@ def main(argv):
     options = set(('extendedglobalexpr','extendedtypecast','extendedassignment',
         'allowkeyconcat','allowmultistrings','processpre','warntabs','optimize',
         'optsigns','optfloats','constfold','dcr','errmissingdefault',
+        'listlength',
         ))
 
     assert not (options - validoptions), (u"Default options not present in"