diff --git a/src/specify_cli/workflows/engine.py b/src/specify_cli/workflows/engine.py
index d17513cc0b..c78fd62352 100644
--- a/src/specify_cli/workflows/engine.py
+++ b/src/specify_cli/workflows/engine.py
@@ -851,7 +851,32 @@ def load(cls, run_id: str, project_root: Path) -> RunState:
             installed_origin_tracked=has_installed_workflow_id,
         )
         state.status = RunStatus(state_data["status"])
-        state.current_step_index = state_data.get("current_step_index", 0)
+
+        # ``resume()`` slices ``definition.steps[state.current_step_index :]``
+        # with no guard of its own -- unlike ``workflow_id`` /
+        # ``installed_workflow_id`` / ``installed_registry_root`` / ``inputs``
+        # above, this field was never shape-checked here. A non-int value (a
+        # hand-edited or externally-written state.json, e.g. a string or
+        # float) reaches that slice and raises a raw, unhelpful
+        # ``TypeError: slice indices must be integers or None or have an
+        # __index__ method`` from deep inside ``resume()`` instead of the
+        # clean "Invalid run state: ..." this loader already gives every
+        # other malformed field. A negative value slices from the end instead
+        # of failing, silently resuming from the wrong step. Reject both here,
+        # consistent with the sibling checks. ``bool`` is an ``int`` subclass,
+        # so it is excluded explicitly (mirrors the ``max_iterations`` /
+        # ``continue_on_error`` bool guards elsewhere in this module).
+        current_step_index = state_data.get("current_step_index", 0)
+        if (
+            isinstance(current_step_index, bool)
+            or not isinstance(current_step_index, int)
+            or current_step_index < 0
+        ):
+            raise ValueError(
+                "Invalid run state: 'current_step_index' must be a "
+                f"non-negative integer, got {current_step_index!r}"
+            )
+        state.current_step_index = current_step_index
         state.current_step_id = state_data.get("current_step_id")
         state.step_results = state_data.get("step_results", {})
         state.workflow_dir = state_data.get("workflow_dir")
diff --git a/tests/test_workflows.py b/tests/test_workflows.py
index d599f3c6a4..8a72d075cc 100644
--- a/tests/test_workflows.py
+++ b/tests/test_workflows.py
@@ -7376,6 +7376,49 @@ def test_load_rejects_stored_run_id_mismatch(self, project_dir):
         ):
             RunState.load("requested-run", project_dir)
 
+    @pytest.mark.parametrize(
+        "bad_current_step_index",
+        ["not-a-number", 1.5, -1, [0], {"index": 0}, True],
+    )
+    def test_load_rejects_invalid_current_step_index(
+        self, project_dir, bad_current_step_index
+    ):
+        """A malformed ``current_step_index`` must fail at load(), not resume().
+
+        ``resume()`` slices ``definition.steps[state.current_step_index :]``
+        with no guard of its own. Every other field this loader restores
+        (``workflow_id``, ``installed_workflow_id``, ``installed_registry_root``,
+        ``inputs``) is shape-checked here and raises the same clean "Invalid
+        run state: ..." ``ValueError`` on a malformed value; ``current_step_index``
+        was the one field silently passed through. A non-int value reaches the
+        slice and raises a raw, unhelpful ``TypeError`` from deep inside
+        ``resume()`` instead. ``True`` is included because ``bool`` is an
+        ``int`` subclass and would otherwise slip past a bare ``isinstance(...,
+        int)`` check.
+        """
+        from specify_cli.workflows.engine import RunState
+
+        run_dir = (
+            project_dir / ".specify" / "workflows" / "runs" / "bad-index-run"
+        )
+        run_dir.mkdir(parents=True)
+        (run_dir / "state.json").write_text(
+            json.dumps(
+                {
+                    "run_id": "bad-index-run",
+                    "workflow_id": "test-workflow",
+                    "status": "paused",
+                    "current_step_index": bad_current_step_index,
+                }
+            ),
+            encoding="utf-8",
+        )
+
+        with pytest.raises(
+            ValueError, match="'current_step_index' must be a non-negative integer"
+        ):
+            RunState.load("bad-index-run", project_dir)
+
     @pytest.mark.parametrize(
         ("installed_workflow_id", "installed_registry_root"),
         [