diff --git a/src/specify_cli/workflows/steps/prompt/__init__.py b/src/specify_cli/workflows/steps/prompt/__init__.py
index 5bf10fbffc..3bb9a2708c 100644
--- a/src/specify_cli/workflows/steps/prompt/__init__.py
+++ b/src/specify_cli/workflows/steps/prompt/__init__.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import math
 import shutil
 from pathlib import Path
 from typing import Any
@@ -88,6 +89,15 @@ def execute(self, config: dict[str, Any], context: StepContext) -> StepResult:
                 ),
             )
 
+        # An invalid timeout reaches subprocess.run() and raises a raw
+        # TypeError ("unsupported operand type(s) for +: 'float' and 'str'")
+        # or ValueError, which the engine re-raises — taking down the whole
+        # run with a message that names neither the step nor 'timeout'. Fail
+        # this step cleanly instead, mirroring the shell step.
+        timeout_error = self._timeout_error(config)
+        if timeout_error is not None:
+            return StepResult(status=StepStatus.FAILED, error=timeout_error)
+
         # Attempt CLI dispatch
         timeout = config.get("timeout", 300)
         dispatch_result = self._try_dispatch(
@@ -131,6 +141,41 @@ def execute(self, config: dict[str, Any], context: StepContext) -> StepResult:
                 ),
             )
 
+    @staticmethod
+    def _timeout_error(config: dict[str, Any]) -> str | None:
+        """Return an error message if ``config['timeout']`` is invalid, else None.
+
+        Shared by execute() and validate() so both paths reject the same
+        values with the same message, mirroring the shell step. An absent
+        ``timeout`` is valid (the default is used). bool is a subclass of int,
+        but ``timeout: true`` is a config error rather than a duration, so it
+        is rejected explicitly. Non-finite floats (YAML ``.inf``/``.nan``) pass
+        a plain ``> 0`` check but would raise in subprocess.run(), and a
+        non-positive timeout makes subprocess.run() report an immediate
+        TimeoutExpired, so both are rejected too.
+        """
+        if "timeout" not in config:
+            return None
+        timeout = config["timeout"]
+        try:
+            valid_timeout = (
+                not isinstance(timeout, bool)
+                and isinstance(timeout, (int, float))
+                and timeout > 0
+                and math.isfinite(timeout)
+            )
+        except OverflowError:
+            # An int too large to convert to float (e.g. a 400-digit YAML
+            # scalar) clears every clause above and raises here — and would
+            # raise the same from subprocess.run(timeout=...).
+            valid_timeout = False
+        if not valid_timeout:
+            return (
+                f"Prompt step {config.get('id', '?')!r}: 'timeout' must be a "
+                f"positive number of seconds, got {timeout!r}."
+            )
+        return None
+
     @staticmethod
     def _try_dispatch(
         prompt: str,
@@ -250,4 +295,7 @@ def validate(self, config: dict[str, Any]) -> list[str]:
                 f"Prompt step {config.get('id', '?')!r}: 'model' must be a "
                 f"string, got {type(model).__name__}."
             )
+        timeout_error = self._timeout_error(config)
+        if timeout_error is not None:
+            errors.append(timeout_error)
         return errors
diff --git a/tests/test_workflows.py b/tests/test_workflows.py
index 6e191fe799..bc6893e9d9 100644
--- a/tests/test_workflows.py
+++ b/tests/test_workflows.py
@@ -1705,6 +1705,90 @@ def test_execute_falsey_non_string_integration_fails_loudly(self, falsey):
         assert res.status is StepStatus.FAILED, falsey
         assert "'model' must be a string" in (res.error or ""), falsey
 
+    @pytest.mark.parametrize(
+        "bad", ["30", True, float("inf"), float("nan"), 0, -5, ["30"], None, 10**400]
+    )
+    def test_validate_rejects_invalid_timeout(self, bad):
+        """'timeout' reaches subprocess.run(), so validate() must reject junk.
+
+        The sibling shell step already rejects exactly these values; the
+        prompt step gained a ``timeout`` without the matching guard, so a
+        workflow that fails validation as a shell step passed as a prompt one.
+
+        ``10**400`` is an int too large to convert to float: it passes
+        ``isinstance``/``> 0`` but makes ``math.isfinite()`` — and later
+        ``subprocess.run()`` — raise ``OverflowError``, so the guard has to
+        catch that rather than let it escape as the crash it exists to stop.
+        """
+        from specify_cli.workflows.steps.prompt import PromptStep
+
+        step = PromptStep()
+        errors = step.validate(
+            {"id": "p", "type": "prompt", "prompt": "hi", "timeout": bad}
+        )
+        assert any("'timeout' must be a positive number" in e for e in errors), (
+            bad,
+            errors,
+        )
+
+    @pytest.mark.parametrize("good", [300, 5, 0.5])
+    def test_validate_accepts_valid_timeout(self, good):
+        """A positive int/float timeout — and an absent one — stay valid."""
+        from specify_cli.workflows.steps.prompt import PromptStep
+
+        step = PromptStep()
+        for config in (
+            {"id": "p", "type": "prompt", "prompt": "hi", "timeout": good},
+            {"id": "p", "type": "prompt", "prompt": "hi"},
+        ):
+            errors = step.validate(config)
+            assert not any("'timeout'" in e for e in errors), (config, errors)
+
+    def test_execute_fails_cleanly_on_invalid_timeout(self, monkeypatch):
+        """execute() must fail the step, not raise, on an invalid timeout.
+
+        The engine does not auto-validate step config and re-raises anything a
+        step throws, so an unvalidated ``timeout`` reaching subprocess.run()
+        raised a raw ``TypeError: unsupported operand type(s) for +: 'float'
+        and 'str'`` (or ``ValueError`` for NaN) that aborted the entire run —
+        naming neither the step nor the field — after earlier steps had
+        already run their side effects.
+        """
+        import subprocess
+        from unittest.mock import patch
+
+        from specify_cli.workflows.steps.prompt import PromptStep
+        from specify_cli.workflows.base import StepContext, StepStatus
+
+        def fail_if_called(*args, **kwargs):
+            raise AssertionError("subprocess.run should not run on invalid timeout")
+
+        monkeypatch.setattr(subprocess, "run", fail_if_called)
+        step = PromptStep()
+        ctx = StepContext(inputs={}, default_integration="claude")
+        # A string/list raises TypeError and NaN raises ValueError inside
+        # subprocess.run(); ``True`` would silently become a 1s timeout (bool
+        # is an int subclass); a non-positive value reports an immediate
+        # TimeoutExpired for a command that never got the time to run; an int
+        # too large to convert to float raises OverflowError.
+        for bad in ("30", True, float("nan"), 0, -5, ["30"], 10**400):
+            with patch(
+                "specify_cli.workflows.steps.prompt.shutil.which",
+                return_value="/opt/claude",
+            ):
+                result = step.execute(
+                    {
+                        "id": "p",
+                        "type": "prompt",
+                        "prompt": "hi",
+                        "integration": "claude",
+                        "timeout": bad,
+                    },
+                    ctx,
+                )
+            assert result.status is StepStatus.FAILED, bad
+            assert "'timeout' must be a positive number" in (result.error or ""), bad
+
 
 class TestShellStep:
     """Test the shell step type."""