diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 0a6b199bf..29aa11035 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1751,9 +1751,9 @@ void ExprCall::eval(EvalState & state, Env & env, Value & v)
     // 4: about 60
     // 5: under 10
     // This excluded attrset lambdas (`{...}:`). Contributions of mixed lambdas appears insignificant at ~150 total.
-    SmallValueVector<4> vArgs(args.size());
-    for (size_t i = 0; i < args.size(); ++i)
-        vArgs[i] = args[i]->maybeThunk(state, env);
+    SmallValueVector<4> vArgs(args->size());
+    for (size_t i = 0; i < args->size(); ++i)
+        vArgs[i] = (*args)[i]->maybeThunk(state, env);
 
     state.callFunction(vFun, vArgs, v, pos);
 }
diff --git a/src/libexpr/include/nix/expr/nixexpr.hh b/src/libexpr/include/nix/expr/nixexpr.hh
index 5121b9d98..e4880a3fb 100644
--- a/src/libexpr/include/nix/expr/nixexpr.hh
+++ b/src/libexpr/include/nix/expr/nixexpr.hh
@@ -592,7 +592,10 @@ public:
 struct ExprCall : Expr
 {
     Expr * fun;
-    std::pmr::vector<Expr *> args;
+    /**
+     * args will never be null. See comment on ExprAttrs::AttrDefs below.
+     */
+    std::optional<std::pmr::vector<Expr *>> args;
     PosIdx pos;
     std::optional<PosIdx> cursedOrEndPos; // used during parsing to warn about https://github.com/NixOS/nix/issues/11118
 
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 3de5bdcb8..34d286f4e 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -191,7 +191,7 @@ void ExprCall::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << '(';
     fun->show(symbols, str);
-    for (auto e : args) {
+    for (auto e : *args) {
         str << ' ';
         e->show(symbols, str);
     }
@@ -490,7 +490,7 @@ void ExprCall::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
         es.exprEnvs.insert(std::make_pair(this, env));
 
     fun->bindVars(es, env);
-    for (auto e : args)
+    for (auto e : *args)
         e->bindVars(es, env);
 }
 
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index c4333eced..a9166c5b5 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -115,7 +115,7 @@ static void setDocPosition(const LexerState & lexerState, ExprLambda * lambda, P
 
 static Expr * makeCall(Exprs & exprs, PosIdx pos, Expr * fn, Expr * arg) {
     if (auto e2 = dynamic_cast<ExprCall *>(fn)) {
-        e2->args.push_back(arg);
+        e2->args->push_back(arg);
         return fn;
     }
     return exprs.add<ExprCall>(pos, fn, {arg});