diff --git a/packages/compiler/src/backend/llvm/lib-filesystem.ts b/packages/compiler/src/backend/llvm/lib-filesystem.ts
index 1083c69d5..b1d8869fd 100644
--- a/packages/compiler/src/backend/llvm/lib-filesystem.ts
+++ b/packages/compiler/src/backend/llvm/lib-filesystem.ts
@@ -746,6 +746,8 @@ export function emitPathUrlLibCall(host: LlvmEmitterContext, e: LibCallExpr): Ll
     const dict = B.tmp();
     B.line(`${dict} = call ptr @${mangleRecordNew(e.type.shapeId)}()`);
     const out = host.own({ name: dict, type: e.type });
+    // Node builds the result with a null prototype.
+    B.line(`store i8 1, ptr ${host.recordMapFlagsPtr(dict, e.type.shapeId)}`);
     const ovf = host.recordOvfPtr(dict, e.type.shapeId);
     B.line(
       `call void @scr_qs_parse_into(ptr ${ovf}, ptr ${args[0]!.name}, ptr ${args[1]!.name}, ptr ${args[2]!.name}, double ${args[3]!.name}, i32 ${strTag}, i32 ${arrTag})`,
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/5842-qs-parse-null-prototype.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/5842-qs-parse-null-prototype.ts.json
new file mode 100644
index 000000000..a5b4a3e21
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/5842-qs-parse-null-prototype.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/5842-qs-parse-null-prototype.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/5843-qs-parse-null-prototype-js.mjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/5843-qs-parse-null-prototype-js.mjs.json
new file mode 100644
index 000000000..228f0a4c0
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/5843-qs-parse-null-prototype-js.mjs.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/5843-qs-parse-null-prototype-js.mjs"
+ ],
+ "diags": []
+}
diff --git a/tests/corpus/5842-qs-parse-null-prototype.ts b/tests/corpus/5842-qs-parse-null-prototype.ts
new file mode 100644
index 000000000..02d5cc134
--- /dev/null
+++ b/tests/corpus/5842-qs-parse-null-prototype.ts
@@ -0,0 +1,34 @@
+// querystring.parse and querystring.decode return a null-prototype
+// object: inspection prints the "[Object: null prototype]" base,
+// getPrototypeOf answers null, and ToPrimitive and Object.prototype
+// methods throw TypeErrors. Spread copies keep Object.prototype.
+import * as qs from "node:querystring";
+import { inspect } from "node:util";
+
+const parsed = qs.parse("a=1&b=2&b=3&c");
+console.log(parsed);
+console.log(inspect(parsed), inspect({ nested: parsed }), inspect([qs.parse("")]));
+console.log(qs.decode("x=1;y=2", ";"));
+console.log(Object.getPrototypeOf(parsed) === null, Object.keys(parsed), JSON.stringify(parsed));
+
+const attempt = (label: string, f: () => unknown): void => {
+  try {
+    console.log(label, f());
+  } catch (e) {
+    console.log(label, (e as Error).name, (e as Error).message);
+  }
+};
+attempt("String", () => String(parsed));
+attempt("template", () => `${parsed}`);
+attempt("concat", () => "q=" + parsed);
+attempt("hasOwnProperty", () => parsed.hasOwnProperty("a"));
+attempt("toString", () => parsed.toString());
+console.log(Object.prototype.toString.call(parsed), Object.hasOwn(parsed, "b"));
+console.log(Object.prototype.hasOwnProperty.call(parsed, "c"));
+
+const copy = { ...parsed };
+console.log(copy, Object.getPrototypeOf(copy) === Object.prototype, String(copy));
+
+parsed.added = "yes";
+delete parsed.a;
+console.log(parsed, parsed.b, parsed.added);
diff --git a/tests/corpus/5843-qs-parse-null-prototype-js.mjs b/tests/corpus/5843-qs-parse-null-prototype-js.mjs
new file mode 100644
index 000000000..676d188c4
--- /dev/null
+++ b/tests/corpus/5843-qs-parse-null-prototype-js.mjs
@@ -0,0 +1,12 @@
+// querystring.parse results keep their null prototype when they cross into
+// checked-dynamic values in a JavaScript module: inspection, getPrototypeOf,
+// ToPrimitive and the `in` operator.
+import qs from "node:querystring";
+const parsed = qs.parse("a=1&b=2&b=3");
+const holder = { parsed, list: [parsed] };
+console.log(holder);
+const dyn = JSON.parse("{}");
+dyn.p = parsed;
+console.log(dyn, Object.getPrototypeOf(dyn.p) === null);
+try { console.log(String(dyn.p)); } catch (e) { console.log(e.name, e.message); }
+console.log("toString" in parsed, "a" in parsed);
diff --git a/tests/harness/corpus-costs.json b/tests/harness/corpus-costs.json
index e2645a7a8..c09013aba 100644
--- a/tests/harness/corpus-costs.json
+++ b/tests/harness/corpus-costs.json
@@ -1849,6 +1849,8 @@
     "5836-url-search-params-tuple-pairs.ts": 2118,
     "5837-util-format-json-circular.ts": 3117,
     "5838-qs-stringify-bigint.ts": 2207,
+    "5842-qs-parse-null-prototype.ts": 1774,
+    "5843-qs-parse-null-prototype-js.mjs": 1559,
     "5858-disposable-stack.ts": 3050,
     "5859-disposable-stack-js.js": 3100,
     "5881-inspect-weak-collections.ts": 2615,
@@ -4509,6 +4511,8 @@
     "5836-url-search-params-tuple-pairs.ts": 3193,
     "5837-util-format-json-circular.ts": 3408,
     "5838-qs-stringify-bigint.ts": 3519,
+    "5842-qs-parse-null-prototype.ts": 7077,
+    "5843-qs-parse-null-prototype-js.mjs": 5395,
     "5858-disposable-stack.ts": 3750,
     "5859-disposable-stack-js.js": 3600,
     "5881-inspect-weak-collections.ts": 2915,