diff --git a/packages/cli/src/commands/iterate-options.ts b/packages/cli/src/commands/iterate-options.ts
index 200575b4..7e1a25fc 100644
--- a/packages/cli/src/commands/iterate-options.ts
+++ b/packages/cli/src/commands/iterate-options.ts
@@ -1,6 +1,12 @@
 import { InvalidArgumentError } from 'commander';
 
 export function parsePositiveSafeInteger(value: string): number {
+  // Only accept plain decimal digit strings. Number() would otherwise coerce
+  // scientific ("1e2"), hexadecimal ("0x10"), binary/octal, signed ("+60"), and
+  // whitespace-padded values into numbers, which are not valid interval inputs.
+  if (!/^\d+$/.test(value)) {
+    throw new InvalidArgumentError('must be a positive safe integer');
+  }
   const parsed = Number(value);
   if (!Number.isSafeInteger(parsed) || parsed < 1) {
     throw new InvalidArgumentError('must be a positive safe integer');
diff --git a/packages/cli/src/commands/iterate.test.ts b/packages/cli/src/commands/iterate.test.ts
index 4892cab6..e9f9011d 100644
--- a/packages/cli/src/commands/iterate.test.ts
+++ b/packages/cli/src/commands/iterate.test.ts
@@ -12,6 +12,13 @@ describe('parsePositiveSafeInteger', () => {
       expect(() => parsePositiveSafeInteger(value)).toThrow('positive safe integer');
     },
   );
+
+  it.each(['1e2', '0x10', '0b10', '0o10', '+60', ' 60', '60 ', '1_000'])(
+    'rejects non-decimal numeric interval %s',
+    (value) => {
+      expect(() => parsePositiveSafeInteger(value)).toThrow('positive safe integer');
+    },
+  );
 });
 
 describe('parseQuietHours', () => {