diff --git a/.flake8 b/.flake8
index b42cf528..66efd2c7 100644
--- a/.flake8
+++ b/.flake8
@@ -10,6 +10,11 @@ rst-directives = deprecated
 per-file-ignores =
     # More specific globs seem to overwrite the more generic ones so we have
     # to split them out by directory
+    # So if you have a rule like:
+    # tests/*: D102,D103
+    # and a rule like:
+    # tests/test_hey.py: D102
+    # THEN, test_hey.py will NOT be excluding D103
 
     # asserts are ok in tests
     tests/*:S101,D102,D103
@@ -34,4 +39,4 @@ per-file-ignores =
     # and ignore long comment line
     src/spiffworkflow_backend/services/logging_service.py:N802,B950
 
-    tests/spiffworkflow_backend/integration/test_process_api.py:S607,S101,D103,S605
+    tests/spiffworkflow_backend/integration/test_process_api.py:S607,S101,S605,D102,D103,D101
diff --git a/src/spiffworkflow_backend/routes/process_instances_controller.py b/src/spiffworkflow_backend/routes/process_instances_controller.py
index 1271f929..679c2fa7 100644
--- a/src/spiffworkflow_backend/routes/process_instances_controller.py
+++ b/src/spiffworkflow_backend/routes/process_instances_controller.py
@@ -72,6 +72,18 @@ def process_instance_create(
     process_model_identifier = _un_modify_modified_process_model_id(
         modified_process_model_identifier
     )
+
+    process_model = _get_process_model(process_model_identifier)
+    if process_model.primary_file_name is None:
+        raise ApiError(
+            error_code="process_model_missing_primary_bpmn_file",
+            message=(
+                f"Process Model '{process_model_identifier}' does not have a primary"
+                " bpmn file. One must be set in order to instantiate this model."
+            ),
+            status_code=400,
+        )
+
     process_instance = (
         ProcessInstanceService.create_process_instance_from_process_model_identifier(
             process_model_identifier, g.user
diff --git a/src/spiffworkflow_backend/routes/process_models_controller.py b/src/spiffworkflow_backend/routes/process_models_controller.py
index 694c01ef..19f064c9 100644
--- a/src/spiffworkflow_backend/routes/process_models_controller.py
+++ b/src/spiffworkflow_backend/routes/process_models_controller.py
@@ -277,6 +277,17 @@ def process_model_file_delete(
     """Process_model_file_delete."""
     process_model_identifier = modified_process_model_identifier.replace(":", "/")
     process_model = _get_process_model(process_model_identifier)
+    if process_model.primary_file_name == file_name:
+        raise ApiError(
+            error_code="process_model_file_cannot_be_deleted",
+            message=(
+                f"'{file_name}' is the primary bpmn file for"
+                f" '{process_model_identifier}' and cannot be deleted. Please set"
+                " another file as the primary before attempting to delete this one."
+            ),
+            status_code=400,
+        )
+
     try:
         SpecFileService.delete_file(process_model, file_name)
     except FileNotFoundError as exception:
diff --git a/tests/spiffworkflow_backend/integration/test_process_api.py b/tests/spiffworkflow_backend/integration/test_process_api.py
index ebc26ac6..7213e31c 100644
--- a/tests/spiffworkflow_backend/integration/test_process_api.py
+++ b/tests/spiffworkflow_backend/integration/test_process_api.py
@@ -922,6 +922,28 @@ class TestProcessApi(BaseTest):
         assert response.json is not None
         assert response.json["error_code"] == "process_model_file_cannot_be_found"
 
+    def test_process_model_file_delete_when_primary_file(
+        self,
+        app: Flask,
+        client: FlaskClient,
+        with_db_and_bpmn_file_cleanup: None,
+        with_super_admin_user: UserModel,
+    ) -> None:
+        process_model_identifier = self.create_group_and_model_with_bpmn(
+            client, with_super_admin_user
+        )
+        modified_process_model_identifier = process_model_identifier.replace("/", ":")
+
+        response = client.delete(
+            f"/v1.0/process-models/{modified_process_model_identifier}/files/random_fact.bpmn",
+            follow_redirects=True,
+            headers=self.logged_in_headers(with_super_admin_user),
+        )
+
+        assert response.status_code == 400
+        assert response.json is not None
+        assert response.json["error_code"] == "process_model_file_cannot_be_deleted"
+
     def test_process_model_file_delete(
         self,
         app: Flask,
@@ -935,8 +957,16 @@ class TestProcessApi(BaseTest):
         )
         modified_process_model_identifier = process_model_identifier.replace("/", ":")
 
+        self.create_spec_file(
+            client,
+            process_model_id=process_model_identifier,
+            file_name="second_file.json",
+            file_data=b"<h1>HEY</h1>",
+            user=with_super_admin_user,
+        )
+
         response = client.delete(
-            f"/v1.0/process-models/{modified_process_model_identifier}/files/random_fact.bpmn",
+            f"/v1.0/process-models/{modified_process_model_identifier}/files/second_file.json",
             follow_redirects=True,
             headers=self.logged_in_headers(with_super_admin_user),
         )
@@ -946,7 +976,7 @@ class TestProcessApi(BaseTest):
         assert response.json["ok"]
 
         response = client.get(
-            f"/v1.0/process-models/{modified_process_model_identifier}/files/random_fact.svg",
+            f"/v1.0/process-models/{modified_process_model_identifier}/files/second_file.json",
             headers=self.logged_in_headers(with_super_admin_user),
         )
         assert response.status_code == 404