diff --git a/airflow/api_fastapi/common/parameters.py b/airflow/api_fastapi/common/parameters.py
index 6bfbfadf4180c..7554ee88450bb 100644
--- a/airflow/api_fastapi/common/parameters.py
+++ b/airflow/api_fastapi/common/parameters.py
@@ -33,7 +33,7 @@
     overload,
 )
 
-from fastapi import Depends, HTTPException, Query
+from fastapi import Depends, HTTPException, Query, status
 from pendulum.parsing.exceptions import ParserError
 from pydantic import AfterValidator, BaseModel, NonNegativeInt
 from sqlalchemy import Column, case, or_
@@ -337,9 +337,15 @@ def to_orm(self, select: Select) -> Select:
 
     @staticmethod
     def _convert_dag_run_states(states: Iterable[str] | None) -> list[DagRunState | None] | None:
-        if not states:
-            return None
-        return [None if s in ("none", None) else DagRunState(s) for s in states]
+        try:
+            if not states:
+                return None
+            return [None if s in ("none", None) else DagRunState(s) for s in states]
+        except ValueError:
+            raise HTTPException(
+                status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+                detail=f"Invalid value for state. Valid values are {', '.join(DagRunState)}",
+            )
 
     def depends(self, state: list[str] = Query(default_factory=list)) -> DagRunStateFilter:
         states = self._convert_dag_run_states(state)
@@ -360,7 +366,13 @@ def to_orm(self, select: Select) -> Select:
         return select.where(or_(*conditions))
 
     def depends(self, state: list[str] = Query(default_factory=list)) -> TIStateFilter:
-        states = _convert_ti_states(state)
+        try:
+            states = _convert_ti_states(state)
+        except ValueError:
+            raise HTTPException(
+                status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+                detail=f"Invalid value for state. Valid values are {', '.join(TaskInstanceState)}",
+            )
         return self.set_value(states)
 
 
diff --git a/tests/api_fastapi/core_api/routes/public/test_dag_run.py b/tests/api_fastapi/core_api/routes/public/test_dag_run.py
index 2ac22a02e31aa..b3ce267bf5222 100644
--- a/tests/api_fastapi/core_api/routes/public/test_dag_run.py
+++ b/tests/api_fastapi/core_api/routes/public/test_dag_run.py
@@ -425,8 +425,11 @@ def test_bad_filters(self, test_client):
         assert body["detail"] == expected_detail
 
     def test_invalid_state(self, test_client):
-        with pytest.raises(ValueError, match="'invalid' is not a valid DagRunState"):
-            test_client.get(f"/public/dags/{DAG1_ID}/dagRuns", params={"state": "invalid"})
+        response = test_client.get(f"/public/dags/{DAG1_ID}/dagRuns", params={"state": ["invalid"]})
+        assert response.status_code == 422
+        assert (
+            response.json()["detail"] == f"Invalid value for state. Valid values are {', '.join(DagRunState)}"
+        )
 
 
 class TestPatchDagRun:
diff --git a/tests/api_fastapi/core_api/routes/public/test_task_instances.py b/tests/api_fastapi/core_api/routes/public/test_task_instances.py
index f8e75600171b3..b3b4d0ffb1b50 100644
--- a/tests/api_fastapi/core_api/routes/public/test_task_instances.py
+++ b/tests/api_fastapi/core_api/routes/public/test_task_instances.py
@@ -956,6 +956,14 @@ def test_not_found(self, test_client):
         assert response.status_code == 404
         assert response.json() == {"detail": "DagRun with run_id: `invalid` was not found"}
 
+    def test_bad_state(self, test_client):
+        response = test_client.get("/public/dags/~/dagRuns/~/taskInstances", params={"state": "invalid"})
+        assert response.status_code == 422
+        assert (
+            response.json()["detail"]
+            == f"Invalid value for state. Valid values are {', '.join(TaskInstanceState)}"
+        )
+
     @pytest.mark.xfail(reason="permissions not implemented yet.")
     def test_return_TI_only_from_readable_dags(self, test_client, session):
         task_instances = {