diff --git a/src/cli/environmentCommands.ts b/src/cli/environmentCommands.ts
index fa3eab11bb..238ea53c46 100644
--- a/src/cli/environmentCommands.ts
+++ b/src/cli/environmentCommands.ts
@@ -38,6 +38,7 @@ import { inspectWebNetworkCaptureInputSchema } from "../domain/webNetworkCapture
 import { withCommandCancellation } from "./commandCancellation.js";
 import { finishAnalysisCommand } from "./finishAnalysisCommand.js";
 import type { CliInstance } from "./types.js";
+import { cliDecimalField } from "./options.js";
 
 /** Same envelope label as the other JSON-input commands and `parseCliJsonInput`. */
 const cliError = (error: AnalysisError): JsonValue => ({
@@ -512,8 +513,10 @@ const registerBuildCommand = (
         .boolean()
         .default(false)
         .describe("Run every stage and report, but write nothing"),
-      captureTimeoutMs:
+      // Decimal tokens only: numeric coercion would read "0x1" as 1 ms.
+      captureTimeoutMs: cliDecimalField(
         inspectWebNetworkCaptureInputSchema.shape.capture_timeout_ms,
+      ),
     }),
     run: ({ args, options }) =>
       withCommandCancellation((signal) =>
diff --git a/src/cli/webNetworkCaptureCommands.ts b/src/cli/webNetworkCaptureCommands.ts
index b31296d907..9cffd44753 100644
--- a/src/cli/webNetworkCaptureCommands.ts
+++ b/src/cli/webNetworkCaptureCommands.ts
@@ -8,7 +8,7 @@ import { CLI_COMMANDS } from "../cliCommandNames.js";
 import { logCliCommand } from "../cliLogging.js";
 import type { Logger } from "pino";
 import type { CliInstance } from "./types.js";
-import { cliIntegerArgument } from "./options.js";
+import { cliDecimalField, cliIntegerArgument } from "./options.js";
 import { withCommandCancellation } from "./commandCancellation.js";
 import {
   analysisEvidenceDeliveryOptions,
@@ -55,8 +55,10 @@ export const registerWebNetworkCaptureCommands = (
         .optional()
         .describe("Zero-based producer ordinals; repeat to select several"),
       ...explicitSensitiveValueOptions,
-      captureTimeoutMs:
+      // Decimal tokens only: numeric coercion would read "0x1" as 1 ms.
+      captureTimeoutMs: cliDecimalField(
         inspectWebNetworkCaptureInputSchema.shape.capture_timeout_ms,
+      ),
     }),
     run: ({ args, options }) =>
       withCommandCancellation((signal) =>
diff --git a/tests/boundary/cli/environmentBuildCli.test.ts b/tests/boundary/cli/environmentBuildCli.test.ts
index 712b49edc6..8f2377923c 100644
--- a/tests/boundary/cli/environmentBuildCli.test.ts
+++ b/tests/boundary/cli/environmentBuildCli.test.ts
@@ -152,7 +152,13 @@ cliTest(
     const har = join(root, "grafana.har");
     await writeFile(har, JSON.stringify(environmentManifestHar()));
     const planned = await cli.run({
-      arguments: ["environment-build", har, "--dry-run", "--json"],
+      arguments: [
+        "environment-build",
+        har,
+        "--dry-run",
+        "--capture-timeout-ms=030000",
+        "--json",
+      ],
       timeoutMs: 60_000,
     });
     expect(planned.exitCode, planned.stderr).toBe(0);
@@ -188,6 +194,22 @@ cliTest(
     expect(conflicting.exitCode).toBe(1);
     expect(conflicting.json).toMatchObject({ code: "invalid_request" });
 
+    // Both capture readers share the field. Numeric coercion would read
+    // "0x1" as a 1 ms capture deadline.
+    for (const command of [
+      ["environment-build", har, "--dry-run"],
+      ["inspect-web-network-capture", har, "har"],
+    ]) {
+      const hexDeadline = await cli.run({
+        arguments: [...command, "--capture-timeout-ms=0x1", "--json"],
+      });
+      expect(hexDeadline.exitCode).toBe(1);
+      expect(hexDeadline.json).toMatchObject({
+        code: "VALIDATION_ERROR",
+        fieldErrors: [expect.objectContaining({ path: "captureTimeoutMs" })],
+      });
+    }
+
     const noDirectory = await cli.run({
       arguments: ["environment-build", har, "--json"],
       timeoutMs: 60_000,