diff --git a/packages/compiler/src/frontend/lowering/lower-functions.ts b/packages/compiler/src/frontend/lowering/lower-functions.ts
index ea7d7957b..c1cca9c64 100644
--- a/packages/compiler/src/frontend/lowering/lower-functions.ts
+++ b/packages/compiler/src/frontend/lowering/lower-functions.ts
@@ -893,6 +893,9 @@ export function blockedBodyDiagnostics(
   lowerer.fnStack.push(ctx);
   let internal = false;
   try {
+    // A declared `this` parameter gives the body its receiver, as
+    // lowerFunction declares it.
+    if (decl.parameters.nodes.some(isThisParameter)) declareCallReceiver(lowerer, decl, false);
     for (const param of decl.parameters.nodes) {
       if (isThisParameter(param)) continue;
       const declaredParam = lowersCleanly(lowerer, () => {
diff --git a/packages/runtime/src/scr_json.c b/packages/runtime/src/scr_json.c
index 906be0ccd..fbfcade66 100644
--- a/packages/runtime/src/scr_json.c
+++ b/packages/runtime/src/scr_json.c
@@ -3968,10 +3968,14 @@ bool scr_bytes_instanceof_at(const ScrDyn *value, const ScrDyn *callee, const Sc
     bool undefined_prototype = prototype->kind == SCR_DYN_UNDEF;
     scr_dyn_release(prototype);
     /* A function the program compiled with no prototype (an arrow function
-     * or a method): Node's TypeError for an object, false for a primitive.
-     * The runtime's own constructors carry "native:" signatures. */
+     * or a method): false for a primitive, and Node's TypeError for every
+     * object, typed arrays, native handles, promises and typed references
+     * included. The runtime's own constructors carry "native:" signatures. */
     if (undefined_prototype && (!callee->v.fn.sig || strncmp(callee->v.fn.sig, "native:", 7) != 0)) {
-      if (value->kind != SCR_DYN_OBJ && value->kind != SCR_DYN_ARR && value->kind != SCR_DYN_FUNC) return false;
+      if (value->kind == SCR_DYN_UNDEF || value->kind == SCR_DYN_NULL || value->kind == SCR_DYN_BOOL ||
+          value->kind == SCR_DYN_NUM || value->kind == SCR_DYN_STR || value->kind == SCR_DYN_BIGINT ||
+          value->kind == SCR_DYN_SYMBOL)
+        return false;
       static const char message[] = "Function has non-object prototype 'undefined' in instanceof check";
       scr_throw_error_msg(SCR_ERR_TYPE, message, sizeof message - 1);
       return false;
diff --git a/tests/corpus/7005-dyn-constructor-instanceof/main.ts b/tests/corpus/7005-dyn-constructor-instanceof/main.ts
index c32a820c2..21fcbbd26 100644
--- a/tests/corpus/7005-dyn-constructor-instanceof/main.ts
+++ b/tests/corpus/7005-dyn-constructor-instanceof/main.ts
@@ -3,9 +3,10 @@
 // an ES5 constructor's prototype, at module load and in calls, and throws a
 // TypeError for an arrow function, which has no prototype, when the value
 // is an object.
-import { arrowCheck, describe, rejects, tags } from "tag-types";
+import { arrowCheck, arrowObjects, describe, rejects, tags } from "tag-types";
 
 console.log(tags());
 console.log(describe("{}"), describe("[1]"), describe("null"), describe('"s"'));
 console.log(rejects('{"tag":"!x"}'));
 console.log(arrowCheck("{}"), arrowCheck("1"));
+console.log(arrowObjects());
diff --git a/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.d.ts b/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.d.ts
index adeea728e..5b451adfa 100644
--- a/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.d.ts
+++ b/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.d.ts
@@ -2,3 +2,4 @@ export declare function describe(json: string): string;
 export declare function tags(): string;
 export declare function rejects(json: string): string;
 export declare function arrowCheck(json: string): string;
+export declare function arrowObjects(): string;
diff --git a/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.js b/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.js
index 20eee362f..81165bd58 100644
--- a/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.js
+++ b/tests/corpus/7005-dyn-constructor-instanceof/node_modules/tag-types/index.js
@@ -59,3 +59,13 @@ module.exports.arrowCheck = function (json) {
     return error.name + ": " + error.message;
   }
 };
+// Every object reaches the TypeError, typed arrays, promises and Maps too.
+module.exports.arrowObjects = function () {
+  return [new Uint8Array(2), Promise.resolve(1), new Map(), [1]].map(function (value) {
+    try {
+      return String(value instanceof make);
+    } catch (error) {
+      return error.name;
+    }
+  }).join(",");
+};
diff --git a/tests/coverage-fixtures/blocked-signature-body.ts b/tests/coverage-fixtures/blocked-signature-body.ts
index 7f8db4eb8..2c37484e0 100644
--- a/tests/coverage-fixtures/blocked-signature-body.ts
+++ b/tests/coverage-fixtures/blocked-signature-body.ts
@@ -13,3 +13,7 @@ function unused(target: WeakRef<object>): number {
   return extra === undefined ? 0 : 1;
 }
 console.log(measure(new WeakRef({}), "abc"));
+// A declared `this` parameter gives the body its receiver.
+function described(this: { label: string }, target: WeakRef<object>): string {
+  return this.label + String(target);
+}
diff --git a/tests/harness/coverage.test.ts b/tests/harness/coverage.test.ts
index 40b55b078..3ed562aea 100644
--- a/tests/harness/coverage.test.ts
+++ b/tests/harness/coverage.test.ts
@@ -194,17 +194,21 @@ test("the body of a signature-blocked function reports its diagnostics", () => {
     "SC2020 'WeakRef<object>' is part of the standard library types but has no scriptc lowering yet",
     "SC2020 'new WeakRef' is part of the standard library types but has no scriptc lowering yet",
   ]);
-  // Nothing calls unused: its signature and body report as unreached.
+  // Nothing calls unused or described: their signatures and bodies report
+  // as unreached. described's declared `this` is its receiver, so
+  // `this.label` reports nothing.
   expect(sites(coverage.unreached?.diagnostics ?? [])).toEqual([
     "SC2004 uses of 'extra' inherit the blocker on its declaration",
+    "SC2004 uses of 'target' inherit the blocker on its declaration",
+    "SC2020 'WeakRef<object>' is part of the standard library types but has no scriptc lowering yet",
     "SC2020 'WeakRef<object>' is part of the standard library types but has no scriptc lowering yet",
     "SC2020 'new WeakRef' is part of the standard library types but has no scriptc lowering yet",
   ]);
   // The bodies' statements still count once each, as not static.
   const un = coverage.unreached?.stats;
-  expect(coverage.stats.functionsSkipped + (un?.functionsSkipped ?? 0)).toBe(2);
-  expect(coverage.stats.statementsTotal + (un?.statementsTotal ?? 0)).toBe(6);
-  expect(coverage.stats.statementsFailed + (un?.statementsFailed ?? 0)).toBe(6);
+  expect(coverage.stats.functionsSkipped + (un?.functionsSkipped ?? 0)).toBe(3);
+  expect(coverage.stats.statementsTotal + (un?.statementsTotal ?? 0)).toBe(7);
+  expect(coverage.stats.statementsFailed + (un?.statementsFailed ?? 0)).toBe(7);
 });
 
 test("deferred fences in a module's top-level code report as running at startup", () => {