diff --git a/src/cli.ts b/src/cli.ts
index 67c072dc047..021fadf880a 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -310,15 +310,15 @@ export const createCli = (
       // Incur's `mcp add` silently skips a valued option with no value and
       // swallows the next flag as the value: the registration succeeds without
       // the requested agent or command. Reject a trailing --agent/--command/-c,
-      // a value position occupied by another flag, and an empty `--flag=` form
-      // up front.
+      // a value position occupied by another flag, an empty `--flag=` form,
+      // and a separate empty-string value up front.
       const valued = ["--agent", "--command", "-c"];
       let missingValue: string | undefined;
       for (let index = 0; index < command.length; index += 1) {
         const next = command[index + 1];
         if (
           valued.includes(command[index]!) &&
-          (next === undefined || next.startsWith("-"))
+          (next === undefined || next === "" || next.startsWith("-"))
         ) {
           missingValue = command[index];
           break;
diff --git a/tests/boundary/cli/mcpAddOptionValidation.test.ts b/tests/boundary/cli/mcpAddOptionValidation.test.ts
index f9ef5555883..7e8bbe7d068 100644
--- a/tests/boundary/cli/mcpAddOptionValidation.test.ts
+++ b/tests/boundary/cli/mcpAddOptionValidation.test.ts
@@ -46,6 +46,30 @@ cliTest("mcp add rejects valued options without a value", async ({ cli }) => {
     });
   }
 
+  // A separate empty string is not a value either; without this check Incur
+  // silently registers with defaults. REA rejects it before registration.
+  for (const [flag, field] of [
+    ["--agent", "agent"],
+    ["--command", "command"],
+    ["-c", "command"],
+  ] as const) {
+    const result = await run(["mcp", "add", flag, ""]);
+    expect(result.exitCode, result.stderr).toBe(1);
+    expect(result.json).toMatchObject({
+      code: "VALIDATION_ERROR",
+      fieldErrors: expect.arrayContaining([
+        expect.objectContaining({
+          code: "invalid_value",
+          missing: false,
+          path: field,
+        }),
+      ]),
+    });
+    await expect(access(settingsPath(home))).rejects.toMatchObject({
+      code: "ENOENT",
+    });
+  }
+
   // Incur would swallow the following flag as the option value; REA rejects it.
   const swallowed = await run(["mcp", "add", "--command", "--agent", "amp"]);
   expect(swallowed.exitCode, swallowed.stderr).toBe(1);