diff --git a/packages/compiler/src/frontend/lowering/call-arguments.ts b/packages/compiler/src/frontend/lowering/call-arguments.ts
index b02d0b85c..a139bfc64 100644
--- a/packages/compiler/src/frontend/lowering/call-arguments.ts
+++ b/packages/compiler/src/frontend/lowering/call-arguments.ts
@@ -421,12 +421,16 @@ export function completeArgs(
     ) {
       const stmts: IrStmt[] = [];
       const values = restNodes.map((a): IrExpr => {
+        // A tuple field is read where its spread appears: a later
+        // argument may write the tuple.
+        let value: IrExpr;
         if (isIr(a)) {
-          if (a.ir.kind !== "seqExpr") return a.ir;
-          stmts.push(...a.ir.stmts);
-          return a.ir.result;
-        }
-        const value = lowerer.lowerExpr(a as ts.Expression);
+          value = a.ir;
+          if (value.kind === "seqExpr") {
+            stmts.push(...value.stmts);
+            value = value.result;
+          }
+        } else value = lowerer.lowerExpr(a as ts.Expression);
         const saved = lowerer.declareHiddenLocal("%callArg", value.type);
         stmts.push({ kind: "varDecl", localId: saved.id, init: value, loc: value.loc });
         return { kind: "varRef", localId: saved.id, type: value.type, loc: value.loc };
diff --git a/tests/corpus/8004-optional-element-conversions.ts b/tests/corpus/8004-optional-element-conversions.ts
index 2a394c331..07178e9b0 100644
--- a/tests/corpus/8004-optional-element-conversions.ts
+++ b/tests/corpus/8004-optional-element-conversions.ts
@@ -33,6 +33,22 @@ function label(first: string, ...rest: (string | undefined)[]): string {
 }
 const words: [string, string | undefined, string | undefined] = ["a", undefined, "c"];
 console.log(label(...words), label("b", undefined));
+// Spread tuple fields are read before later arguments run.
+const changing: [boolean, boolean | undefined] = [true, undefined];
+function flip(pair: [boolean, boolean | undefined], second: boolean | undefined): boolean {
+  pair[0] = !pair[0];
+  pair[1] = second;
+  return pair[0];
+}
+console.log(flags(...changing, flip(changing, true)));
+console.log(flags(...changing, flip(changing, undefined), ...changing));
+const swapped: [string, string | undefined] = ["x", "y"];
+function swap(pair: [string, string | undefined]): string {
+  pair[0] = "w";
+  pair[1] = undefined;
+  return "v";
+}
+console.log(label("z", ...swapped, swap(swapped), ...swapped));
 
 function pick(start: (number | undefined)[] | string[], other: (number | undefined)[] | string[]): string {
   let a = start;