diff --git a/changelog/344.bugfix.md b/changelog/344.bugfix.md
new file mode 100644
index 000000000..8fd221485
--- /dev/null
+++ b/changelog/344.bugfix.md
@@ -0,0 +1 @@
+Fix a bug in the `FormValidationAction` which immediately deactivated the form.
diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 445709f4d..64e3d4ecf 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -681,12 +681,17 @@ def _get_entity_type_of_slot_to_fill(
 class FormValidationAction(Action, ABC):
     """A helper class for slot validations and extractions of custom slots."""
 
+    def form_name(self) -> Text:
+        """Returns the form's name."""
+        return self.name().replace("validate_", "", 1)
+
     async def run(
         self,
         dispatcher: "CollectingDispatcher",
         tracker: "Tracker",
         domain: "DomainDict",
     ) -> List[EventType]:
+        """Runs the custom actions. Please the docstring of the parent class."""
         extraction_events = await self.extract_custom_slots(dispatcher, tracker, domain)
         tracker.add_slots(extraction_events)
 
@@ -812,7 +817,7 @@ def slots_mapped_in_domain(self, domain: "DomainDict") -> List[Text]:
         Returns:
             Slot names mapped in the domain.
         """
-        return list(domain.get("forms", {}).get(self.name(), {}).keys())
+        return list(domain.get("forms", {}).get(self.form_name(), {}).keys())
 
     async def validate(
         self,
@@ -832,7 +837,7 @@ async def validate(
         """
         slots: Dict[Text, Any] = tracker.slots_to_validate()
 
-        for slot_name, slot_value in slots.items():
+        for slot_name, slot_value in list(slots.items()):
             method_name = f"validate_{slot_name.replace('-','_')}"
             validate_method = getattr(self, method_name, None)
 
diff --git a/tests/test_forms.py b/tests/test_forms.py
index efb1574f4..b6878a601 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -1503,10 +1503,10 @@ def test_form_deprecation():
 
 class TestFormValidationAction(FormValidationAction):
     def __init__(self, form_name: Text = "some_form") -> None:
-        self.form_name = form_name
+        self.name_of_form = form_name
 
     def name(self) -> Text:
-        return self.form_name
+        return self.name_of_form
 
     def validate_slot1(
         self,
@@ -1643,6 +1643,48 @@ async def test_form_validation_without_validate_function():
     ]
 
 
+async def test_form_validation_changing_slots_during_validation():
+    form_name = "some_form"
+
+    class TestForm(FormValidationAction):
+        def name(self) -> Text:
+            return form_name
+
+        async def validate_my_slot(
+            self,
+            slot_value: Any,
+            dispatcher: "CollectingDispatcher",
+            tracker: "Tracker",
+            domain: "DomainDict",
+        ) -> Dict[Text, Any]:
+            return {"my_slot": None, "other_slot": "value"}
+
+    form = TestForm()
+
+    # tracker with active form
+    tracker = Tracker(
+        "default",
+        {},
+        {},
+        [SlotSet("my_slot", "correct_value")],
+        False,
+        None,
+        {"name": form_name, "is_interrupted": False, "rejected": False},
+        "action_listen",
+    )
+
+    dispatcher = CollectingDispatcher()
+    events = await form.run(
+        dispatcher=dispatcher,
+        tracker=tracker,
+        domain={"forms": {form_name: {"my_slot": []}}},
+    )
+    assert events == [
+        SlotSet("my_slot", None),
+        SlotSet("other_slot", "value"),
+    ]
+
+
 async def test_form_validation_dash_slot():
     form_name = "some_form"