diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index cf307d820..983491a31 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -60,7 +60,6 @@ void copyContext(const Value & v, PathSet & context);
 typedef std::map<Path, StorePath> SrcToStore;
 
 
-std::ostream & printValue(const EvalState & state, std::ostream & str, const Value & v);
 std::string printValue(const EvalState & state, const Value & v);
 std::ostream & operator << (std::ostream & os, const ValueType t);