1 files changed, 3 insertions, 1 deletions
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index d070fdab8..8355e443e 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -83,6 +83,8 @@ struct PrimOp
     void check();
 };
 
+std::ostream & operator<<(std::ostream & output, PrimOp & primOp);
+
 /**
  * Info about a constant
  */
@@ -126,7 +128,7 @@ std::unique_ptr<ValMap> mapStaticEnvBindings(const SymbolTable & st, const Stati
 void copyContext(const Value & v, NixStringContext & context);
 
 
-std::string printValue(const EvalState & state, const Value & v);
+std::string printValue(EvalState & state, Value & v);
 std::ostream & operator << (std::ostream & os, const ValueType t);