diff --git a/src/native/parsers/demangle.test.ts b/src/native/parsers/demangle.test.ts
index 5b15229bd..dd17e34aa 100644
--- a/src/native/parsers/demangle.test.ts
+++ b/src/native/parsers/demangle.test.ts
@@ -40,21 +40,23 @@ describe("parseDemangledSymbols", () => {
     ]);
   });
 
-  it("identifies invalid Swift symbols that fail demangling", () => {
-    const inputs = ["$sInvalidMangle", "_$sAlsoInvalid"];
-    const output = "$sInvalidMangle\n_$sAlsoInvalid\n";
-    expect(parseDemangledSymbols(inputs, output)).toEqual([
-      {
-        input: "$sInvalidMangle",
-        output: "$sInvalidMangle",
-        status: "invalid",
-      },
-      {
-        input: "_$sAlsoInvalid",
-        output: "_$sAlsoInvalid",
-        status: "invalid",
-      },
-    ]);
+  it("identifies invalid Swift symbols for every demangler mangling prefix", () => {
+    const inputs = [
+      "_T0Bogus",
+      "$SBogus",
+      "_$SBogus",
+      "$sBogus",
+      "_$sBogus",
+      "@__swiftmacro_Bogus",
+      "$eBogus",
+      "_$eBogus",
+      "_Tprintf",
+    ];
+    expect(
+      parseDemangledSymbols(inputs, `${inputs.join("\n")}\n`).map(
+        ({ status }) => status,
+      ),
+    ).toEqual([...Array<string>(8).fill("invalid"), "unchanged"]);
   });
 
   it("parses mixed batches preserving ordering", () => {
diff --git a/src/native/parsers/demangle.ts b/src/native/parsers/demangle.ts
index afcb30b62..6f1e42d61 100644
--- a/src/native/parsers/demangle.ts
+++ b/src/native/parsers/demangle.ts
@@ -8,6 +8,22 @@ const resultSchema = z.object({
 
 export type DemangledSymbol = z.infer<typeof resultSchema>;
 
+/**
+ * Prefixes the Swift demangler accepts as mangled names (Swift 4, 4.x, 5+,
+ * macro file names and Embedded Swift). Legacy `_T` is omitted because it is
+ * also an ordinary C symbol spelling such as `_Tprintf`.
+ */
+const SWIFT_MANGLING_PREFIXES = [
+  "_T0",
+  "$S",
+  "_$S",
+  "$s",
+  "_$s",
+  "@__swiftmacro_",
+  "$e",
+  "_$e",
+] as const;
+
 /**
  * Preserve input ordering while parsing `swift-demangle --compact` lines.
  * The demangler ends each record with LF, so a carriage return belongs to the
@@ -33,7 +49,7 @@ export const parseDemangledSymbols = (
       output: value,
       status:
         value === input
-          ? input.startsWith("$s") || input.startsWith("_$s")
+          ? SWIFT_MANGLING_PREFIXES.some((prefix) => input.startsWith(prefix))
             ? "invalid"
             : "unchanged"
           : "demangled",
diff --git a/tests/boundary/mcp/nativeDemangleMcp.test.ts b/tests/boundary/mcp/nativeDemangleMcp.test.ts
index 8e66a27fa..b6ad1d02c 100644
--- a/tests/boundary/mcp/nativeDemangleMcp.test.ts
+++ b/tests/boundary/mcp/nativeDemangleMcp.test.ts
@@ -68,5 +68,39 @@ describe.skipIf(process.platform !== "darwin")(
         );
       },
     );
+
+    mcpTest(
+      "reports undecodable symbols with any Swift mangling prefix as invalid",
+      async ({ mcp, onTestFinished }) => {
+        const target = join(
+          await createTestTempDirectory("rea-demangle-mcp-"),
+          "tool",
+        );
+        await copyFile("/usr/bin/true", target);
+        const client = await openProductionTarget(mcp, onTestFinished, target);
+        const prefixes = ["_T0", "$S", "_$S", "$e", "_$e"];
+
+        const called = await client.callTool({
+          name: "demangle_swift",
+          arguments: {
+            symbols: [
+              ...prefixes.map((prefix) => `${prefix}4main3FooV`),
+              ...prefixes.map((prefix) => `${prefix}Bogus`),
+              "_Tprintf",
+            ],
+          },
+        });
+        expect(called.isError, JSON.stringify(called.content)).not.toBe(true);
+        expect(
+          demangledSchema
+            .parse(called.structuredContent)
+            .normalized_result.symbols.map(({ status }) => status),
+        ).toEqual([
+          ...prefixes.map(() => "demangled"),
+          ...prefixes.map(() => "invalid"),
+          "unchanged",
+        ]);
+      },
+    );
   },
 );