1 files changed, 1 insertions, 1 deletions
diff --git a/rule.h b/rule.h
index 4d72bb7..84412c1 100644
--- a/rule.h
+++ b/rule.h
@@ -65,7 +65,7 @@ struct RuleVarAssignment {
 // |term| is '='), |after_term_fn| will be called to obtain the right
 // hand side.
 void ParseRule(Loc& loc, StringPiece line, char term,
-               function<string()> after_term_fn,
+               const function<string()> &after_term_fn,
                Rule** rule, RuleVarAssignment* rule_var);
 
 #endif  // RULE_H_