diff --git a/Include/grammar.h b/Include/grammar.h
index faccae4..4b66b1e 100644
--- a/Include/grammar.h
+++ b/Include/grammar.h
@@ -66,7 +66,7 @@
 } grammar;
 
 /* FUNCTIONS */
-dfa *PyGrammar_FindDFA(grammar *g, int type);
+const dfa *PyGrammar_FindDFA(grammar *g, int type);
 const char *PyGrammar_LabelRepr(label *lb);
 void PyGrammar_AddAccelerators(grammar *g);
 void PyGrammar_RemoveAccelerators(grammar *);