diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index f9bff7b98..37018007f 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -148,7 +148,7 @@ PosIdx Value::determinePos(const PosIdx pos) const
     switch (internalType) {
         case tAttrs: return attrs()->pos;
         case tLambda: return lambda().fun->pos;
-        case tApp: return payload.app.left->determinePos(pos);
+        case tApp: return app().left->determinePos(pos);
         default: return pos;
     }
     #pragma GCC diagnostic pop
diff --git a/src/libexpr/include/nix/expr/eval-inline.hh b/src/libexpr/include/nix/expr/eval-inline.hh
index 97bf71a6b..7d13d7cc7 100644
--- a/src/libexpr/include/nix/expr/eval-inline.hh
+++ b/src/libexpr/include/nix/expr/eval-inline.hh
@@ -106,7 +106,7 @@ void EvalState::forceValue(Value & v, const PosIdx pos)
         }
     }
     else if (v.isApp())
-        callFunction(*v.payload.app.left, *v.payload.app.right, v, pos);
+        callFunction(*v.app().left, *v.app().right, v, pos);
 }
 
 
diff --git a/src/libexpr/include/nix/expr/value.hh b/src/libexpr/include/nix/expr/value.hh
index 797e31191..d25511c45 100644
--- a/src/libexpr/include/nix/expr/value.hh
+++ b/src/libexpr/include/nix/expr/value.hh
@@ -491,6 +491,9 @@ public:
 
     FunctionApplicationThunk primOpApp() const
     { return payload.primOpApp; }
+
+    FunctionApplicationThunk app() const
+    { return payload.app; }
 };