diff --git a/lark/common.py b/lark/common.py
index 2c940bd..f9b0990 100644
--- a/lark/common.py
+++ b/lark/common.py
@@ -1,4 +1,5 @@
 import re
+import sre_parse
 
 class GrammarError(Exception):
     pass
@@ -57,9 +58,9 @@ class Pattern(object):
 
     # Pattern Hashing assumes all subclasses have a different priority!
     def __hash__(self):
-        return hash((self.priority, self.value))
+        return hash((type(self), self.value))
     def __eq__(self, other):
-        return self.priority == other.priority and self.value == other.value
+        return type(self) == type(other) and self.value == other.value
 
     def _get_flags(self):
         if self.flags:
@@ -71,13 +72,21 @@ class PatternStr(Pattern):
     def to_regexp(self):
         return self._get_flags() + re.escape(self.value)
 
-    priority = 0
+    @property
+    def min_width(self):
+        return len(self.value)
+    max_width = min_width
 
 class PatternRE(Pattern):
     def to_regexp(self):
         return self._get_flags() + self.value
 
-    priority = 1
+    @property
+    def min_width(self):
+        return sre_parse.parse(self.to_regexp()).getwidth()[0]
+    @property
+    def max_width(self):
+        return sre_parse.parse(self.to_regexp()).getwidth()[1]
 
 class TokenDef(object):
     def __init__(self, name, pattern):
diff --git a/lark/lexer.py b/lark/lexer.py
index 86d976f..4e6d5b9 100644
--- a/lark/lexer.py
+++ b/lark/lexer.py
@@ -1,7 +1,6 @@
 ## Lexer Implementation
 
 import re
-import sre_parse
 
 from .utils import Str, classify
 from .common import is_terminal, PatternStr, PatternRE, TokenDef
@@ -120,8 +119,7 @@ class Lexer(object):
             except:
                 raise LexError("Cannot compile token %s: %s" % (t.name, t.pattern))
 
-            width = sre_parse.parse(t.pattern.to_regexp()).getwidth()
-            if width[0] == 0:
+            if t.pattern.min_width == 0:
                 raise LexError("Lexer does not allow zero-width tokens. (%s: %s)" % (t.name, t.pattern))
 
         token_names = {t.name for t in tokens}
@@ -133,7 +131,7 @@ class Lexer(object):
         self.newline_types = [t.name for t in tokens if _regexp_has_newline(t.pattern.to_regexp())]
         self.ignore_types = [t for t in ignore]
 
-        tokens.sort(key=lambda x:(x.pattern.priority, len(x.pattern.value)), reverse=True)
+        tokens.sort(key=lambda x:x.pattern.max_width, reverse=True)
 
         tokens, self.callback = _create_unless(tokens)
         assert all(self.callback.values())