diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 591aa6583..cd7d19747 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -786,9 +786,9 @@ void Value::mkString(std::string_view s, const PathSet & context)
 }
 
 
-void mkPath(Value & v, const char * s)
+void Value::mkPath(std::string_view s)
 {
-    v.mkPath(dupString(s));
+    mkPath(dupStringWithLen(s.data(), s.size()));
 }
 
 
@@ -1711,8 +1711,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
     else if (firstType == nPath) {
         if (!context.empty())
             throwEvalError(pos, "a string that refers to a store path cannot be appended to a path");
-        auto path = canonPath(s.str());
-        mkPath(v, path.c_str());
+        v.mkPath(canonPath(s.str()));
     } else
         v.mkString(s.str(), context);
 }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 57be5ac23..650200ae4 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1441,7 +1441,7 @@ static void prim_dirOf(EvalState & state, const Pos & pos, Value * * args, Value
 {
     PathSet context;
     Path dir = dirOf(state.coerceToString(pos, *args[0], context, false, false));
-    if (args[0]->type() == nPath) mkPath(v, dir.c_str()); else v.mkString(dir, context);
+    if (args[0]->type() == nPath) v.mkPath(dir); else v.mkString(dir, context);
 }
 
 static RegisterPrimOp primop_dirOf({
@@ -1522,7 +1522,7 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
 
     string path = state.forceStringNoCtx(*args[1], pos);
 
-    mkPath(v, state.checkSourcePath(state.findFile(searchPath, path, pos)).c_str());
+    v.mkPath(state.checkSourcePath(state.findFile(searchPath, path, pos)));
 }
 
 static RegisterPrimOp primop_findFile(RegisterPrimOp::Info {
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 3f9b65197..ba647a10d 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -248,6 +248,8 @@ public:
         path = s;
     }
 
+    void mkPath(std::string_view s);
+
     inline void mkNull()
     {
         clearValue();
@@ -399,9 +401,6 @@ static inline void mkString(Value & v, const Symbol & s)
 }
 
 
-void mkPath(Value & v, const char * s);
-
-
 #if HAVE_BOEHMGC
 typedef std::vector<Value *, traceable_allocator<Value *> > ValueVector;
 typedef std::map<Symbol, Value *, std::less<Symbol>, traceable_allocator<std::pair<const Symbol, Value *> > > ValueMap;