diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 5122bd145..5b9db6eea 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -455,6 +455,7 @@ Bindings * EvalState::allocBindings(Bindings::size_t capacity)
 
 void EvalState::mkList(Value & v, unsigned int length)
 {
+    clearValue(v);
     v.type = tList;
     v.list.length = length;
     v.list.elems = length ? (Value * *) GC_MALLOC(length * sizeof(Value *)) : 0;
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 408b5e087..5f18f629e 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -96,7 +96,7 @@ struct Value
    Value to ensure that the target isn't kept alive unnecessarily. */
 static inline void clearValue(Value & v)
 {
-    v.app.right = 0;
+    v.app.left = v.app.right = 0;
 }
 
 
@@ -118,8 +118,8 @@ static inline void mkBool(Value & v, bool b)
 
 static inline void mkNull(Value & v)
 {
+    clearValue(v);
     v.type = tNull;
-    v.app.left = v.app.right = 0; // scrub
 }