diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 0000000..0a92f19
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,4 @@
+[report]
+exclude_lines =
+	pragma: no cover
+	raise NotImplementedError()
diff --git a/.gitignore b/.gitignore
index f7f7bd9..3da2db3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,9 +4,11 @@
 *.dll
 *.egg
 *.egg-info
+.coverage
 .DS_Store
 __pycache__
 build
 dist
 docs/_build
 scripts/*.log
+htmlcov/
diff --git a/CHANGELOG b/CHANGELOG
index 4f4f77b..d733cee 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -10,6 +10,9 @@ v0.4 (unreleased):
   option, RECURSE_OTHERS, which recurses over all children except instances of
   'forcetype' (for example, `code.filter_templates(code.RECURSE_OTHERS)`
   returns all un-nested templates).
+- If something goes wrong while parsing, ParserError will now be raised.
+  Previously, the parser would produce an unclear BadRoute exception or allow
+  an incorrect node tree to be build.
 - Fixed a parser bug involving nested tags.
 - Updated and fixed some documentation.
 
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 0576d29..a530733 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -18,6 +18,9 @@ Unreleased
   which recurses over all children except instances of *forcetype* (for
   example, ``code.filter_templates(code.RECURSE_OTHERS)`` returns all un-nested
   templates).
+- If something goes wrong while parsing, :py:exc:`.ParserError` will now be
+  raised. Previously, the parser would produce an unclear :py:exc:`.BadRoute`
+  exception or allow an incorrect node tree to be build.
 - Fixed a parser bug involving nested tags.
 - Updated and fixed some documentation.
 
diff --git a/mwparserfromhell/nodes/__init__.py b/mwparserfromhell/nodes/__init__.py
index 223cc67..d6f60bd 100644
--- a/mwparserfromhell/nodes/__init__.py
+++ b/mwparserfromhell/nodes/__init__.py
@@ -55,8 +55,8 @@ class Node(StringMixIn):
         raise NotImplementedError()
 
     def __children__(self):
-        return  # Funny generator-that-yields-nothing syntax
-        yield
+        return
+        yield  # pragma: no cover (this is a generator that yields nothing)
 
     def __strip__(self, normalize, collapse):
         return None
diff --git a/mwparserfromhell/parser/__init__.py b/mwparserfromhell/parser/__init__.py
index 8bac295..467d5df 100644
--- a/mwparserfromhell/parser/__init__.py
+++ b/mwparserfromhell/parser/__init__.py
@@ -26,6 +26,19 @@ modules: the :py:mod:`~.tokenizer` and the :py:mod:`~.builder`. This module
 joins them together under one interface.
 """
 
+class ParserError(Exception):
+    """Exception raised when an internal error occurs while parsing.
+
+    This does not mean that the wikicode was invalid, because invalid markup
+    should still be parsed correctly. This means that the parser caught itself
+    with an impossible internal state and is bailing out before other problems
+    can happen. Its appearance indicates a bug.
+    """
+    def __init__(self, extra):
+        msg = "This is a bug and should be reported. Info: {0}.".format(extra)
+        super(ParserError, self).__init__(msg)
+
+
 from .builder import Builder
 from .tokenizer import Tokenizer
 try:
@@ -35,15 +48,22 @@ except ImportError:
     CTokenizer = None
     use_c = False
 
-__all__ = ["use_c", "Parser"]
+__all__ = ["use_c", "Parser", "ParserError"]
 
 class Parser(object):
     """Represents a parser for wikicode.
 
     Actual parsing is a two-step process: first, the text is split up into a
-    series of tokens by the :py:class:`~.Tokenizer`, and then the tokens are
-    converted into trees of :py:class:`~.Wikicode` objects and
-    :py:class:`~.Node`\ s by the :py:class:`~.Builder`.
+    series of tokens by the :py:class:`.Tokenizer`, and then the tokens are
+    converted into trees of :py:class:`.Wikicode` objects and
+    :py:class:`.Node`\ s by the :py:class:`.Builder`.
+
+    Instances of this class or its dependents (:py:class:`.Tokenizer` and
+    :py:class:`.Builder`) should not be shared between threads.
+    :py:meth:`parse` can be called multiple times as long as it is not done
+    concurrently. In general, there is no need to do this because parsing
+    should be done through :py:func:`mwparserfromhell.parse`, which creates a
+    new :py:class:`.Parser` object as necessary.
     """
 
     def __init__(self):
@@ -65,6 +85,9 @@ class Parser(object):
 
         If *skip_style_tags* is ``True``, then ``''`` and ``'''`` will not be
         parsed, but instead will be treated as plain text.
+
+        If there is an internal error while parsing, :py:exc:`.ParserError`
+        will be raised.
         """
         tokens = self._tokenizer.tokenize(text, context, skip_style_tags)
         code = self._builder.build(tokens)
diff --git a/mwparserfromhell/parser/builder.py b/mwparserfromhell/parser/builder.py
index 5f8ce45..559bd54 100644
--- a/mwparserfromhell/parser/builder.py
+++ b/mwparserfromhell/parser/builder.py
@@ -22,7 +22,7 @@
 
 from __future__ import unicode_literals
 
-from . import tokens
+from . import tokens, ParserError
 from ..compat import str
 from ..nodes import (Argument, Comment, ExternalLink, Heading, HTMLEntity, Tag,
                      Template, Text, Wikilink)
@@ -33,33 +33,28 @@ from ..wikicode import Wikicode
 __all__ = ["Builder"]
 
 class Builder(object):
-    """Combines a sequence of tokens into a tree of ``Wikicode`` objects.
+    """Builds a tree of nodes out of a sequence of tokens.
 
     To use, pass a list of :py:class:`~.Token`\ s to the :py:meth:`build`
     method. The list will be exhausted as it is parsed and a
-    :py:class:`~.Wikicode` object will be returned.
+    :py:class:`.Wikicode` object containing the node tree will be returned.
     """
 
     def __init__(self):
         self._tokens = []
         self._stacks = []
 
-    def _wrap(self, nodes):
-        """Properly wrap a list of nodes in a ``Wikicode`` object."""
-        return Wikicode(SmartList(nodes))
-
     def _push(self):
         """Push a new node list onto the stack."""
         self._stacks.append([])
 
-    def _pop(self, wrap=True):
+    def _pop(self):
         """Pop the current node list off of the stack.
 
-        If *wrap* is ``True``, we will call :py:meth:`_wrap` on the list.
+        The raw node list is wrapped in a :py:class:`.SmartList` and then in a
+        :py:class:`.Wikicode` object.
         """
-        if wrap:
-            return self._wrap(self._stacks.pop())
-        return self._stacks.pop()
+        return Wikicode(SmartList(self._stacks.pop()))
 
     def _write(self, item):
         """Append a node to the current node list."""
@@ -84,7 +79,7 @@ class Builder(object):
                 self._tokens.append(token)
                 value = self._pop()
                 if key is None:
-                    key = self._wrap([Text(str(default))])
+                    key = Wikicode(SmartList([Text(str(default))]))
                 return Parameter(key, value, showkey)
             else:
                 self._write(self._handle_token(token))
@@ -270,6 +265,8 @@ class Builder(object):
             return self._handle_comment()
         elif isinstance(token, tokens.TagOpenOpen):
             return self._handle_tag(token)
+        err = "_handle_token() got unexpected {0}".format(type(token).__name__)
+        raise ParserError(err)
 
     def build(self, tokenlist):
         """Build a Wikicode object from a list tokens and return it."""
diff --git a/mwparserfromhell/parser/tokenizer.c b/mwparserfromhell/parser/tokenizer.c
index 41ce5ac..6ab8570 100644
--- a/mwparserfromhell/parser/tokenizer.c
+++ b/mwparserfromhell/parser/tokenizer.c
@@ -347,7 +347,7 @@ static PyObject* Tokenizer_pop_keeping_context(Tokenizer* self)
 
 /*
     Fail the current tokenization route. Discards the current
-    stack/context/textbuffer and raises a BadRoute exception.
+    stack/context/textbuffer and sets the BAD_ROUTE flag.
 */
 static void* Tokenizer_fail_route(Tokenizer* self)
 {
@@ -2681,7 +2681,7 @@ static PyObject* Tokenizer_parse(Tokenizer* self, int context, int push)
 */
 static PyObject* Tokenizer_tokenize(Tokenizer* self, PyObject* args)
 {
-    PyObject *text, *temp;
+    PyObject *text, *temp, *tokens;
     int context = 0, skip_style_tags = 0;
 
     if (PyArg_ParseTuple(args, "U|ii", &text, &context, &skip_style_tags)) {
@@ -2704,13 +2704,29 @@ static PyObject* Tokenizer_tokenize(Tokenizer* self, PyObject* args)
         Py_XDECREF(temp);
         self->text = text;
     }
+
     self->head = self->global = self->depth = self->cycles = 0;
     self->length = PyList_GET_SIZE(self->text);
     self->skip_style_tags = skip_style_tags;
-    return Tokenizer_parse(self, context, 1);
+    tokens = Tokenizer_parse(self, context, 1);
+
+    if (!tokens && !PyErr_Occurred()) {
+        if (!ParserError) {
+            if (load_exceptions())
+                return NULL;
+        }
+        if (BAD_ROUTE) {
+            RESET_ROUTE();
+            PyErr_SetString(ParserError, "C tokenizer exited with BAD_ROUTE");
+        }
+        else
+            PyErr_SetString(ParserError, "C tokenizer exited unexpectedly");
+        return NULL;
+    }
+    return tokens;
 }
 
-static int load_entitydefs(void)
+static int load_entities(void)
 {
     PyObject *tempmod, *defmap, *deflist;
     unsigned numdefs, i;
@@ -2814,7 +2830,7 @@ static int load_tokens(void)
     return 0;
 }
 
-static int load_definitions(void)
+static int load_defs(void)
 {
     PyObject *tempmod,
              *globals = PyEval_GetGlobals(),
@@ -2835,6 +2851,29 @@ static int load_definitions(void)
     return 0;
 }
 
+static int load_exceptions(void)
+{
+    PyObject *tempmod, *parsermod,
+             *globals = PyEval_GetGlobals(),
+             *locals = PyEval_GetLocals(),
+             *fromlist = PyList_New(1),
+             *modname = IMPORT_NAME_FUNC("parser");
+    char *name = "mwparserfromhell";
+
+    if (!fromlist || !modname)
+        return -1;
+    PyList_SET_ITEM(fromlist, 0, modname);
+    tempmod = PyImport_ImportModuleLevel(name, globals, locals, fromlist, 0);
+    Py_DECREF(fromlist);
+    if (!tempmod)
+        return -1;
+    parsermod = PyObject_GetAttrString(tempmod, "parser");
+    Py_DECREF(tempmod);
+    ParserError = PyObject_GetAttrString(parsermod, "ParserError");
+    Py_DECREF(parsermod);
+    return 0;
+}
+
 PyMODINIT_FUNC INIT_FUNC_NAME(void)
 {
     PyObject *module;
@@ -2851,9 +2890,7 @@ PyMODINIT_FUNC INIT_FUNC_NAME(void)
     PyDict_SetItemString(TokenizerType.tp_dict, "USES_C", Py_True);
     EMPTY = PyUnicode_FromString("");
     NOARGS = PyTuple_New(0);
-    if (!EMPTY || !NOARGS)
-        INIT_ERROR;
-    if (load_entitydefs() || load_tokens() || load_definitions())
+    if (!EMPTY || !NOARGS || load_entities() || load_tokens() || load_defs())
         INIT_ERROR;
 #ifdef IS_PY3K
     return module;
diff --git a/mwparserfromhell/parser/tokenizer.h b/mwparserfromhell/parser/tokenizer.h
index 032480d..4312e2f 100644
--- a/mwparserfromhell/parser/tokenizer.h
+++ b/mwparserfromhell/parser/tokenizer.h
@@ -62,6 +62,7 @@ static char** entitydefs;
 
 static PyObject* EMPTY;
 static PyObject* NOARGS;
+static PyObject* ParserError;
 static PyObject* definitions;
 
 
@@ -268,6 +269,8 @@ static int Tokenizer_parse_tag(Tokenizer*);
 static PyObject* Tokenizer_parse(Tokenizer*, int, int);
 static PyObject* Tokenizer_tokenize(Tokenizer*, PyObject*);
 
+static int load_exceptions(void);
+
 
 /* Macros for Python 2/3 compatibility: */
 
diff --git a/mwparserfromhell/parser/tokenizer.py b/mwparserfromhell/parser/tokenizer.py
index e69a823..9af9204 100644
--- a/mwparserfromhell/parser/tokenizer.py
+++ b/mwparserfromhell/parser/tokenizer.py
@@ -24,7 +24,7 @@ from __future__ import unicode_literals
 from math import log
 import re
 
-from . import contexts, tokens
+from . import contexts, tokens, ParserError
 from ..compat import htmlentities, range
 from ..definitions import (get_html_tag, is_parsable, is_single,
                            is_single_only, is_scheme)
@@ -1154,4 +1154,7 @@ class Tokenizer(object):
         split = self.regex.split(text)
         self._text = [segment for segment in split if segment]
         self._head = self._global = self._depth = self._cycles = 0
-        return self._parse(context)
+        try:
+            return self._parse(context)
+        except BadRoute:  # pragma: no cover (untestable/exceptional case)
+            raise ParserError("Python tokenizer exited with BadRoute")
diff --git a/mwparserfromhell/parser/tokens.py b/mwparserfromhell/parser/tokens.py
index 40e5158..c7cc3ef 100644
--- a/mwparserfromhell/parser/tokens.py
+++ b/mwparserfromhell/parser/tokens.py
@@ -34,7 +34,7 @@ from ..compat import py3k, str
 
 __all__ = ["Token"]
 
-class Token (dict):
+class Token(dict):
     """A token stores the semantic meaning of a unit of wikicode."""
 
     def __repr__(self):
diff --git a/mwparserfromhell/utils.py b/mwparserfromhell/utils.py
index fd54ad0..8dc5e4e 100644
--- a/mwparserfromhell/utils.py
+++ b/mwparserfromhell/utils.py
@@ -66,7 +66,7 @@ def parse_anything(value, context=0, skip_style_tags=False):
         nodelist = SmartList()
         for item in value:
             nodelist += parse_anything(item, context, skip_style_tags).nodes
+        return Wikicode(nodelist)
     except TypeError:
         error = "Needs string, Node, Wikicode, int, None, or iterable of these, but got {0}: {1}"
         raise ValueError(error.format(type(value).__name__, value))
-    return Wikicode(nodelist)
diff --git a/tests/test_builder.py b/tests/test_builder.py
index c8fdca3..ed306f7 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -30,7 +30,7 @@ except ImportError:
 from mwparserfromhell.nodes import (Argument, Comment, ExternalLink, Heading,
                                     HTMLEntity, Tag, Template, Text, Wikilink)
 from mwparserfromhell.nodes.extras import Attribute, Parameter
-from mwparserfromhell.parser import tokens
+from mwparserfromhell.parser import tokens, ParserError
 from mwparserfromhell.parser.builder import Builder
 
 from ._test_tree_equality import TreeEqualityTestCase, wrap, wraptext
@@ -420,5 +420,11 @@ class TestBuilder(TreeEqualityTestCase):
             named=True)]))])])
         self.assertWikicodeEqual(valid, self.builder.build(test))
 
+    def test_parser_error(self):
+        """test whether ParserError gets thrown for bad input"""
+        msg = r"_handle_token\(\) got unexpected TemplateClose"
+        self.assertRaisesRegexp(
+            ParserError, msg, self.builder.build, [tokens.TemplateClose()])
+
 if __name__ == "__main__":
     unittest.main(verbosity=2)