diff --git a/extensions/matrix/src/cli.test.ts b/extensions/matrix/src/cli.test.ts
index 69d89bfab562..7f748d4160af 100644
--- a/extensions/matrix/src/cli.test.ts
+++ b/extensions/matrix/src/cli.test.ts
@@ -401,6 +401,20 @@ describe("matrix CLI verification commands", () => {
     expect(runMatrixSelfVerificationMock).not.toHaveBeenCalled();
   });
 
+  it("rejects non-positive Matrix self-verification timeout values", async () => {
+    const program = buildProgram();
+
+    await program.parseAsync(["matrix", "verify", "self", "--timeout-ms", "-1"], {
+      from: "user",
+    });
+
+    expect(process.exitCode).toBe(1);
+    expect(consoleErrorMock).toHaveBeenCalledWith(
+      "Self-verification failed: --timeout-ms must be a positive integer",
+    );
+    expect(runMatrixSelfVerificationMock).not.toHaveBeenCalled();
+  });
+
   it("requests Matrix self-verification and prints the follow-up SAS commands", async () => {
     requestMatrixVerificationMock.mockResolvedValue(
       mockMatrixVerificationSummary({
@@ -1076,6 +1090,34 @@ describe("matrix CLI verification commands", () => {
     );
   });
 
+  it("rejects negative Matrix initial sync limits at the CLI boundary", async () => {
+    const program = buildProgram();
+
+    await program.parseAsync(
+      [
+        "matrix",
+        "account",
+        "add",
+        "--homeserver",
+        "https://matrix.example.org",
+        "--user-id",
+        "@ops:example.org",
+        "--password",
+        "secret",
+        "--initial-sync-limit",
+        "-1",
+      ],
+      { from: "user" },
+    );
+
+    expect(process.exitCode).toBe(1);
+    expect(consoleErrorMock).toHaveBeenCalledWith(
+      "Account setup failed: --initial-sync-limit must be a non-negative integer",
+    );
+    expect(matrixSetupValidateInputMock).not.toHaveBeenCalled();
+    expect(matrixRuntimeReplaceConfigFileMock).not.toHaveBeenCalled();
+  });
+
   it("enables E2EE and bootstraps verification from matrix account add", async () => {
     matrixRuntimeLoadConfigMock.mockReturnValue({ channels: {} });
     matrixSetupApplyAccountConfigMock.mockImplementation(
diff --git a/extensions/matrix/src/cli.ts b/extensions/matrix/src/cli.ts
index 37dfd7ded3d7..f9abd5a3664f 100644
--- a/extensions/matrix/src/cli.ts
+++ b/extensions/matrix/src/cli.ts
@@ -232,7 +232,11 @@ function configureCliLogMode(verbose: boolean): void {
   setMatrixSdkConsoleLogging(verbose);
 }
 
-function parseOptionalInt(value: string | undefined, fieldName: string): number | undefined {
+function parseOptionalInt(
+  value: string | undefined,
+  fieldName: string,
+  opts: { min?: number } = {},
+): number | undefined {
   const trimmed = value?.trim();
   if (!trimmed) {
     return undefined;
@@ -244,6 +248,13 @@ function parseOptionalInt(value: string | undefined, fieldName: string): number
   if (parsed === undefined) {
     throw new Error(`${fieldName} must be an integer`);
   }
+  if (opts.min !== undefined && parsed < opts.min) {
+    throw new Error(
+      opts.min === 1
+        ? `${fieldName} must be a positive integer`
+        : `${fieldName} must be a non-negative integer`,
+    );
+  }
   return parsed;
 }
 
@@ -289,6 +300,9 @@ async function addMatrixAccount(params: {
   useEnv?: boolean;
   enableEncryption?: boolean;
 }): Promise<MatrixCliAccountAddResult> {
+  const initialSyncLimit = parseOptionalInt(params.initialSyncLimit, "--initial-sync-limit", {
+    min: 0,
+  });
   const runtime = getMatrixRuntime();
   const cfg = runtime.config.current() as CoreConfig;
   if (!matrixSetupAdapter.applyAccountConfig) {
@@ -305,7 +319,7 @@ async function addMatrixAccount(params: {
     accessToken: params.accessToken,
     password: params.password,
     deviceName: params.deviceName,
-    initialSyncLimit: parseOptionalInt(params.initialSyncLimit, "--initial-sync-limit"),
+    initialSyncLimit,
     useEnv: params.useEnv === true,
   };
   const accountId =
@@ -1159,15 +1173,18 @@ async function runMatrixCliVerificationSummaryCommand(params: {
 async function runMatrixCliSelfVerificationCommand(
   options: MatrixCliSelfVerificationCommandOptions,
 ): Promise<void> {
-  const { accountId, cfg } = resolveMatrixCliAccountContext(options.account);
+  let resolvedAccountId: string | undefined;
   await runMatrixCliCommand({
     verbose: options.verbose === true,
     json: false,
-    run: async () =>
-      await runMatrixSelfVerification({
+    run: async () => {
+      const timeoutMs = parseOptionalInt(options.timeoutMs, "--timeout-ms", { min: 1 });
+      const { accountId, cfg } = resolveMatrixCliAccountContext(options.account);
+      resolvedAccountId = accountId;
+      return await runMatrixSelfVerification({
         accountId,
         cfg,
-        timeoutMs: parseOptionalInt(options.timeoutMs, "--timeout-ms"),
+        timeoutMs,
         onRequested: (summary) => {
           printAccountLabel(accountId);
           printMatrixVerificationSummary(summary);
@@ -1184,7 +1201,8 @@ async function runMatrixCliSelfVerificationCommand(
           console.log("Compare this SAS with the other Matrix client.");
         },
         confirmSas: async () => await promptMatrixVerificationSasMatch(),
-      }),
+      });
+    },
     onText: (summary, verbose) => {
       printMatrixVerificationSummary(summary);
       console.log(`Device verified by owner: ${summary.deviceOwnerVerified ? "yes" : "no"}`);
@@ -1196,6 +1214,7 @@ async function runMatrixCliSelfVerificationCommand(
       console.log("Self-verification complete.");
     },
     onTextError: () => {
+      const accountId = resolvedAccountId ?? options.account;
       printGuidance([
         `Run ${formatMatrixCliCommand("verify self", accountId)} again and accept the request in another verified Matrix client for this account.`,
         `Then run ${formatMatrixCliCommand("verify status --verbose", accountId)} to confirm Cross-signing verified: yes and Signed by owner: yes.`,