diff --git a/spacy/matcher.pyx b/spacy/matcher.pyx
index 5106161a0..84414c255 100644
--- a/spacy/matcher.pyx
+++ b/spacy/matcher.pyx
@@ -436,6 +436,9 @@ cdef class PhraseMatcher:
             abstract_patterns.append([{tag: True} for tag in get_bilou(length)])
         self.matcher.add('Candidate', None, *abstract_patterns)
         self._callbacks = {}
+        
+    def __len__(self):
+        raise NotImplementedError
 
     def __reduce__(self):
         return (self.__class__, (self.vocab,), None, None)