diff --git a/spacy/en.pyx b/spacy/en.pyx
index 785d21e24..dc8465fc9 100644
--- a/spacy/en.pyx
+++ b/spacy/en.pyx
@@ -224,7 +224,7 @@ cdef class English(Language):
     fl_is_digit = Flag_IsDigit
     v_shape = View_WordShape
     def __cinit__(self, name, user_string_features, user_flag_features):
-        self.cache = {}
+        self.cache.set_empty_key(0)
         lang_data = util.read_lang_data(name)
         rules, words, probs, clusters, case_stats, tag_stats = lang_data
         self.lexicon = lang.Lexicon(words, probs, clusters, case_stats, tag_stats,
diff --git a/spacy/lang.pxd b/spacy/lang.pxd
index 20a40d175..988fa715d 100644
--- a/spacy/lang.pxd
+++ b/spacy/lang.pxd
@@ -3,14 +3,52 @@ from libc.stdint cimport uint64_t
 from spacy.word cimport Lexeme
 from spacy.tokens cimport Tokens
 
-
-cdef struct Flags:
-    size_t is_alpha
-    size_t can_noun
+from libcpp.utility cimport pair
+from libcpp.vector cimport vector
+from libc.stdint cimport uint64_t, int64_t
 
 
-cdef struct ViewIDs:
-    size_t canon_form
+cdef extern from "sparsehash/dense_hash_map" namespace "google":
+    cdef cppclass dense_hash_map[K, D]:
+        K& key_type
+        D& data_type
+        pair[K, D]& value_type
+        uint64_t size_type
+        cppclass iterator:
+            pair[K, D]& operator*() nogil
+            iterator operator++() nogil
+            iterator operator--() nogil
+            bint operator==(iterator) nogil
+            bint operator!=(iterator) nogil
+        iterator begin()
+        iterator end()
+        uint64_t size()
+        uint64_t max_size()
+        bint empty()
+        uint64_t bucket_count()
+        uint64_t bucket_size(uint64_t i)
+        uint64_t bucket(K& key)
+        double max_load_factor()
+        void max_load_vactor(double new_grow)
+        double min_load_factor()
+        double min_load_factor(double new_grow)
+        void set_resizing_parameters(double shrink, double grow)
+        void resize(uint64_t n)
+        void rehash(uint64_t n)
+        dense_hash_map()
+        dense_hash_map(uint64_t n)
+        void swap(dense_hash_map&)
+        pair[iterator, bint] insert(pair[K, D]) nogil
+        void set_empty_key(K&)
+        void set_deleted_key(K& key)
+        void clear_deleted_key()
+        void erase(iterator pos)
+        uint64_t erase(K& k)
+        void erase(iterator first, iterator last)
+        void clear()
+        void clear_no_resize()
+        pair[iterator, iterator] equal_range(K& k)
+        D& operator[](K&) nogil
 
 
 cdef class Lexicon:
@@ -27,13 +65,14 @@ cdef class Lexicon:
 
 cdef class Language:
     cdef unicode name
-    cdef dict cache
+    cdef dense_hash_map[uint64_t, size_t] cache
+    cdef size_t cache_size
     cpdef readonly Lexicon lexicon
     cpdef readonly object tokens_class
 
     cpdef Tokens tokenize(self, unicode text)
     cpdef Lexeme lookup(self, unicode text)
 
-    cdef _tokenize(self, Tokens tokens, unicode string)
+    cdef _tokenize(self, Tokens tokens, Py_UNICODE* characters, size_t length)
     cdef list _split(self, unicode string)
     cdef int _split_one(self, unicode word)
diff --git a/spacy/lang.pyx b/spacy/lang.pyx
index 5a7f98948..dd3394152 100644
--- a/spacy/lang.pyx
+++ b/spacy/lang.pyx
@@ -40,7 +40,8 @@ cdef class Language:
         if string_features is None:
             string_features = []
         self.name = name
-        self.cache = {}
+        self.cache.set_empty_key(0)
+        self.cache_size = 0
         lang_data = read_lang_data(name)
         rules, words, probs, clusters, case_stats, tag_stats = lang_data
         self.lexicon = Lexicon(words, probs, clusters, case_stats, tag_stats,
@@ -102,11 +103,10 @@ cdef class Language:
     cdef _tokenize(self, Tokens tokens, Py_UNICODE* characters, size_t length):
         cdef uint64_t hashed = hash64(characters, length * sizeof(Py_UNICODE), 0)
         cdef unicode string
-        cdef LexemeC** lexemes
         cdef bint free_chunk = False
         cdef size_t i = 0
-        if hashed in self.cache:
-            lexemes = <LexemeC**><size_t>self.cache[hashed]
+        cdef LexemeC** lexemes = <LexemeC**>self.cache[hashed]
+        if lexemes is not NULL:
             while lexemes[i] != NULL:
                 tokens.push_back(lexemes[i])
                 i += 1
@@ -121,8 +121,9 @@ cdef class Language:
             # The intuition here is that if an element belongs in the cache, it
             # has several chances to get in. And if the cache is large, we less
             # believe that the element belongs there.
-            if not self.cache or random.random() < (100000.0 / len(self.cache)):
+            if self.cache_size == 0 or random.random() < (100000.0 / self.cache_size):
                 self.cache[hashed] = <size_t>lexemes
+                self.cache_size += 1
             else:
                 free(lexemes)
 
@@ -172,6 +173,7 @@ cdef class Language:
             lexemes[i + 1] = NULL
             hashed = hash64(<Py_UNICODE*>string, len(string) * sizeof(Py_UNICODE), 0)
             self.cache[hashed] = <size_t>lexemes
+            self.cache_size += 1
  
 
 cdef class Lexicon:
diff --git a/spacy/tokens.pxd b/spacy/tokens.pxd
index ccfe45d24..6ac78de1b 100644
--- a/spacy/tokens.pxd
+++ b/spacy/tokens.pxd
@@ -5,7 +5,7 @@ cdef class Tokens:
     cdef size_t size
 
     cdef LexemeC** lexemes
-    cdef push_back(self, LexemeC* lexeme)
+    cdef int push_back(self, LexemeC* lexeme) except -1
 
     cpdef unicode string(self, size_t i)
     cpdef double prob(self, size_t i)
diff --git a/spacy/tokens.pyx b/spacy/tokens.pyx
index 209ae94d6..9ab5170d2 100644
--- a/spacy/tokens.pyx
+++ b/spacy/tokens.pyx
@@ -44,7 +44,7 @@ cdef class Tokens:
     def append(self, Lexeme lexeme):
         self.push_back(lexeme._c)
 
-    cdef push_back(self, LexemeC* lexeme):
+    cdef int push_back(self, LexemeC* lexeme) except -1:
         if (self.size + 1) == self.length:
             self.size *= 2
             self.lexemes = <LexemeC**>realloc(self.lexemes, self.size * sizeof(LexemeC*))