diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 6f82c6c40..7372134e2 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -866,7 +866,7 @@ static void prim_baseNameOf(EvalState & state, const Pos & pos, Value * * args,
 static void prim_dirOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    Path dir = dirOf(state.coerceToPath(pos, *args[0], context));
+    Path dir = dirOf(state.coerceToString(pos, *args[0], context, false, false));
     if (args[0]->type == tPath) mkPath(v, dir.c_str()); else mkString(v, dir, context);
 }
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 04c98dc80..03f0be705 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -167,7 +167,7 @@ Path dirOf(const Path & path)
 {
     Path::size_type pos = path.rfind('/');
     if (pos == string::npos)
-        throw Error(format("invalid file name '%1%'") % path);
+        return ".";
     return pos == 0 ? "/" : Path(path, 0, pos);
 }