diff --git a/parso/_compatibility.py b/parso/_compatibility.py
index 9ddf23d..db411ee 100644
--- a/parso/_compatibility.py
+++ b/parso/_compatibility.py
@@ -36,7 +36,7 @@ except AttributeError:
 def u(string):
     """Cast to unicode DAMMIT!
     Written because Python2 repr always implicitly casts to a string, so we
-    have to cast back to a unicode (and we now that we always deal with valid
+    have to cast back to a unicode (and we know that we always deal with valid
     unicode, because we check that in the beginning).
     """
     if py_version >= 30:
diff --git a/parso/grammar.py b/parso/grammar.py
index 2cf26d7..e5abf81 100644
--- a/parso/grammar.py
+++ b/parso/grammar.py
@@ -73,7 +73,7 @@ class Grammar(object):
             :py:class:`parso.python.tree.Module`.
         """
         if 'start_pos' in kwargs:
-            raise TypeError("parse() got an unexpected keyworda argument.")
+            raise TypeError("parse() got an unexpected keyword argument.")
         return self._parse(code=code, **kwargs)
 
     def _parse(self, code=None, error_recovery=True, path=None,
diff --git a/parso/tree.py b/parso/tree.py
index 72a1494..6108612 100644
--- a/parso/tree.py
+++ b/parso/tree.py
@@ -55,7 +55,6 @@ class NodeOrLeaf(object):
         Returns the node immediately preceding this node in this parent's
         children list. If this node does not have a previous sibling, it is
         None.
-        None.
         """
         # Can't use index(); we need to test by identity
         for i, child in enumerate(self.parent.children):