diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 4398cc951..59623874c 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -779,7 +779,7 @@ static void prim_readFile(EvalState & state, const Pos & pos, Value * * args, Va
     string s = readFile(state.checkSourcePath(path));
     if (s.find((char) 0) != string::npos)
         throw Error(format("the contents of the file ‘%1%’ cannot be represented as a Nix string") % path);
-    mkString(v, s.c_str(), context);
+    mkString(v, s.c_str());
 }