diff --git a/reana_server/rest/workflows.py b/reana_server/rest/workflows.py
index be620e2b..716b247d 100644
--- a/reana_server/rest/workflows.py
+++ b/reana_server/rest/workflows.py
@@ -525,9 +525,6 @@ def create_workflow(user):  # noqa
         if is_uuid_v4(workflow_name):
             return jsonify({"message": "Workflow name cannot be a valid UUIDv4."}), 400
 
-        validate_workflow(reana_spec_file, input_parameters={})
-        workspace_root_path = reana_spec_file.get("workspace", {}).get("root_path")
-
         workflow_engine = reana_spec_file["workflow"]["type"]
         if workflow_engine not in REANA_WORKFLOW_ENGINES:
             raise Exception("Unknown workflow type.")
@@ -536,6 +533,9 @@ def create_workflow(user):  # noqa
             workflow_engine, reana_spec_file.get("inputs", {}).get("options", {})
         )
 
+        workspace_root_path = reana_spec_file.get("workspace", {}).get("root_path")
+        validate_workspace_path(reana_spec_file)
+
         retention_days = reana_spec_file.get("workspace", {}).get("retention_days")
         retention_rules = get_workspace_retention_rules(retention_days)
 
@@ -1230,6 +1230,12 @@ def start_workflow(workflow_id_or_name, user):  # noqa
             )
         if "yadage" in (workflow.type_, restart_type):
             _load_and_save_yadage_spec(workflow, operational_options)
+
+        input_parameters = parameters.get("input_parameters", {})
+        validate_workflow(
+            workflow.reana_specification, input_parameters=input_parameters
+        )
+
         publish_workflow_submission(workflow, user.id_, parameters)
         response = {
             "message": "Workflow submitted.",
diff --git a/tests/test_views.py b/tests/test_views.py
index d0d3ade9..8a49da90 100644
--- a/tests/test_views.py
+++ b/tests/test_views.py
@@ -10,6 +10,7 @@
 
 import copy
 import json
+import logging
 from io import BytesIO
 from uuid import uuid4
 
@@ -134,7 +135,7 @@ def test_create_workflow(
             )
             assert res.status_code == 400
 
-            # not valid specification
+            # not valid specification. but there is no validation
             workflow_specification = {
                 "workflow": {"specification": {}, "type": "serial"},
             }
@@ -147,7 +148,7 @@ def test_create_workflow(
                 },
                 data=json.dumps(workflow_specification),
             )
-            assert res.status_code == 400
+            assert res.status_code == 200
 
             # correct case
             workflow_specification = sample_serial_workflow_in_db.reana_specification
@@ -163,6 +164,33 @@ def test_create_workflow(
             assert res.status_code == 200
 
 
+def test_start_workflow_validates_specification(
+    app, session, default_user, sample_serial_workflow_in_db
+):
+    with app.test_client() as client:
+        sample_serial_workflow_in_db.status = RunStatus.created
+        sample_serial_workflow_in_db.name = "test"
+        workflow_specification = copy.deepcopy(
+            sample_serial_workflow_in_db.reana_specification
+        )
+        workflow_specification["workflow"]["type"] = "unknown"
+        sample_serial_workflow_in_db.reana_specification = workflow_specification
+        session.add(sample_serial_workflow_in_db)
+        session.commit()
+        res = client.post(
+            url_for(
+                "workflows.start_workflow",
+                workflow_id_or_name=str(sample_serial_workflow_in_db.id_),
+            ),
+            headers={"Content-Type": "application/json"},
+            query_string={
+                "access_token": default_user.access_token,
+            },
+            data=json.dumps({}),
+        )
+        assert res.status_code == 400
+
+
 def test_restart_workflow_validates_specification(
     app, session, default_user, sample_serial_workflow_in_db
 ):