diff --git a/docs/grammar.md b/docs/grammar.md
index e532297..1cd72dd 100644
--- a/docs/grammar.md
+++ b/docs/grammar.md
@@ -204,7 +204,7 @@ Each item is one of:
 * `TERMINAL`
 * `"string literal"` or `/regexp literal/`
 * `(item item ..)` - Group items
-* `[item item ..]` - Maybe. Same as `(item item ..)?`, but generates `None` if there is no match
+* `[item item ..]` - Maybe. Same as `(item item ..)?`, but when `maybe_placeholders=True`, generates `None` if there is no match.
 * `item?` - Zero or one instances of item ("maybe")
 * `item*` - Zero or more instances of item
 * `item+` - One or more instances of item
diff --git a/lark/parsers/lalr_puppet.py b/lark/parsers/lalr_puppet.py
index 40cc0c1..35b2250 100644
--- a/lark/parsers/lalr_puppet.py
+++ b/lark/parsers/lalr_puppet.py
@@ -88,6 +88,9 @@ class ParserPuppet(object):
             self._start == other._start
         )
 
+    def __hash__(self):
+        return hash((tuple(self._state_stack), self._start))
+
     def pretty(self):
         """Print the output of ``choices()`` in a way that's easier to read."""
         out = ["Puppet choices:"]