diff --git a/concore_cli/cli.py b/concore_cli/cli.py
index 4b376c9..c3ef2f3 100644
--- a/concore_cli/cli.py
+++ b/concore_cli/cli.py
@@ -167,6 +167,9 @@ def stop():
 @click.option("--once", is_flag=True, help="Print a single snapshot and exit")
 def watch(study_dir, interval, once):
     """Watch a running simulation study for live monitoring"""
+    if interval <= 0:
+        console.print("[red]Error:[/red] --interval must be greater than 0")
+        sys.exit(1)
     try:
         watch_study(study_dir, interval, once, console)
     except Exception as e:
diff --git a/tests/test_cli.py b/tests/test_cli.py
index d746040..8f4506a 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -786,6 +786,24 @@ def test_inspect_missing_source_file(self):
             self.assertEqual(result.exit_code, 0)
             self.assertIn("Missing files", result.output)
 
+    def test_watch_rejects_negative_interval(self):
+        with self.runner.isolated_filesystem(temp_dir=self.temp_dir):
+            os.mkdir("study")
+            result = self.runner.invoke(
+                cli, ["watch", "study", "--interval", "-1"]
+            )
+            self.assertEqual(result.exit_code, 1)
+            self.assertIn("--interval must be greater than 0", result.output)
+
+    def test_watch_rejects_zero_interval(self):
+        with self.runner.isolated_filesystem(temp_dir=self.temp_dir):
+            os.mkdir("study")
+            result = self.runner.invoke(
+                cli, ["watch", "study", "--interval", "0"]
+            )
+            self.assertEqual(result.exit_code, 1)
+            self.assertIn("--interval must be greater than 0", result.output)
+
 
 if __name__ == "__main__":
     unittest.main()