diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 51036a223..badb271f2 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -160,10 +160,10 @@ bool Value::isTrivial() const
         internalType != tApp
         && internalType != tPrimOpApp
         && (internalType != tThunk
-            || (dynamic_cast<ExprAttrs *>(payload.thunk.expr)
-                && ((ExprAttrs *) payload.thunk.expr)->dynamicAttrs.empty())
-            || dynamic_cast<ExprLambda *>(payload.thunk.expr)
-            || dynamic_cast<ExprList *>(payload.thunk.expr));
+            || (dynamic_cast<ExprAttrs *>(thunk().expr)
+                && ((ExprAttrs *) thunk().expr)->dynamicAttrs.empty())
+            || dynamic_cast<ExprLambda *>(thunk().expr)
+            || dynamic_cast<ExprList *>(thunk().expr));
 }
 
 
@@ -2163,7 +2163,7 @@ void EvalState::forceValueDeep(Value & v)
                 try {
                     // If the value is a thunk, we're evaling. Otherwise no trace necessary.
                     auto dts = debugRepl && i.value->isThunk()
-                        ? makeDebugTraceStacker(*this, *i.value->payload.thunk.expr, *i.value->payload.thunk.env, i.pos,
+                        ? makeDebugTraceStacker(*this, *i.value->thunk().expr, *i.value->thunk().env, i.pos,
                             "while evaluating the attribute '%1%'", symbols[i.name])
                         : nullptr;
 
diff --git a/src/libexpr/include/nix/expr/eval-inline.hh b/src/libexpr/include/nix/expr/eval-inline.hh
index 6e5759c0b..97bf71a6b 100644
--- a/src/libexpr/include/nix/expr/eval-inline.hh
+++ b/src/libexpr/include/nix/expr/eval-inline.hh
@@ -89,9 +89,9 @@ Env & EvalState::allocEnv(size_t size)
 void EvalState::forceValue(Value & v, const PosIdx pos)
 {
     if (v.isThunk()) {
-        Env * env = v.payload.thunk.env;
+        Env * env = v.thunk().env;
         assert(env || v.isBlackhole());
-        Expr * expr = v.payload.thunk.expr;
+        Expr * expr = v.thunk().expr;
         try {
             v.mkBlackhole();
             //checkInterrupt();
diff --git a/src/libexpr/include/nix/expr/value.hh b/src/libexpr/include/nix/expr/value.hh
index 26ec5ff38..29f8ac379 100644
--- a/src/libexpr/include/nix/expr/value.hh
+++ b/src/libexpr/include/nix/expr/value.hh
@@ -485,6 +485,9 @@ public:
 
     Lambda lambda() const
     { return payload.lambda; }
+
+    ClosureThunk thunk() const
+    { return payload.thunk; }
 };
 
 
@@ -492,7 +495,7 @@ extern ExprBlackHole eBlackHole;
 
 bool Value::isBlackhole() const
 {
-    return internalType == tThunk && payload.thunk.expr == (Expr*) &eBlackHole;
+    return internalType == tThunk && thunk().expr == (Expr*) &eBlackHole;
 }
 
 void Value::mkBlackhole()