diff -u ply/yacc.py ply.mine/yacc.py
--- ply/yacc.py	2011-02-18 04:52:28.000000000 +0100
+++ ply.mine/yacc.py	2017-03-03 16:01:13.609507492 +0100
@@ -2794,24 +2794,20 @@
 
     # Compute a signature over the grammar
     def signature(self):
+        parts = []
         try:
-            from hashlib import md5
-        except ImportError:
-            from md5 import md5
-        try:
-            sig = md5()
             if self.start:
-                sig.update(self.start.encode('latin-1'))
+                parts.append(self.start)
             if self.prec:
-                sig.update("".join(["".join(p) for p in self.prec]).encode('latin-1'))
+                parts.append(''.join([''.join(p) for p in self.prec]))
             if self.tokens:
-                sig.update(" ".join(self.tokens).encode('latin-1'))
+                parts.append(' '.join(self.tokens))
             for f in self.pfuncs:
                 if f[3]:
-                    sig.update(f[3].encode('latin-1'))
-        except (TypeError,ValueError):
+                    parts.append(f[3])
+        except (TypeError, ValueError):
             pass
-        return sig.digest()
+        return ''.join(parts)
 
     # -----------------------------------------------------------------------------
     # validate_file()