diff --git a/packages/opencloning-db/src/opencloning_db/models.py b/packages/opencloning-db/src/opencloning_db/models.py
index 8ad7939c..be92e8bd 100644
--- a/packages/opencloning-db/src/opencloning_db/models.py
+++ b/packages/opencloning-db/src/opencloning_db/models.py
@@ -14,11 +14,14 @@
     Enum,
     ForeignKey,
     ForeignKeyConstraint,
+    Index,
     Integer,
     JSON,
     Table,
     UniqueConstraint,
     event,
+    select,
+    text,
 )
 
 from sqlalchemy.sql import func
@@ -202,6 +205,15 @@ class Tag(Base):
 
 class InputEntity(Base):
     __tablename__ = 'input_entity'
+    __table_args__ = (
+        Index(
+            'uq_input_entity_template_sequence_workspace_name',
+            'workspace_id',
+            text('lower(name)'),
+            unique=True,
+            postgresql_where=text("type = 'template_sequence'"),
+        ),
+    )
 
     id: Mapped[int] = mapped_column(primary_key=True)
     workspace_id: Mapped[int] = mapped_column(ForeignKey('workspace.id'), nullable=False)
@@ -364,6 +376,37 @@ def to_pydantic_sequence(self) -> opencloning_models.TemplateSequence:
         )
 
 
+def template_sequence_name_taken(
+    session: SASession,
+    *,
+    workspace_id: int,
+    name: str,
+    exclude_id: int | None = None,
+) -> bool:
+    """Return whether another template sequence in the workspace already has this name (case-insensitive)."""
+    stmt = select(TemplateSequence.id).where(
+        TemplateSequence.workspace_id == workspace_id,
+        func.lower(TemplateSequence.name) == name.lower(),
+    )
+    if exclude_id is not None:
+        stmt = stmt.where(TemplateSequence.id != exclude_id)
+    return session.scalar(stmt.limit(1)) is not None
+
+
+def assert_template_sequence_name_available(
+    session: SASession,
+    *,
+    workspace_id: int,
+    name: str,
+    exclude_id: int | None = None,
+) -> None:
+    if template_sequence_name_taken(session, workspace_id=workspace_id, name=name, exclude_id=exclude_id):
+        raise HTTPException(
+            status_code=409,
+            detail=f"Template sequence '{name}' already exists in this workspace",
+        )
+
+
 class Primer(InputEntity):
     __tablename__ = 'primer'
 
diff --git a/packages/opencloning-db/src/opencloning_db/routers/sequences.py b/packages/opencloning-db/src/opencloning_db/routers/sequences.py
index dd16252f..e9ec1923 100644
--- a/packages/opencloning-db/src/opencloning_db/routers/sequences.py
+++ b/packages/opencloning-db/src/opencloning_db/routers/sequences.py
@@ -49,8 +49,10 @@
     Tag,
     SequenceSample,
     SourceInput,
+    TemplateSequence,
     User,
     WorkspaceRole,
+    assert_template_sequence_name_available,
     require_real_sequence,
 )
 from fastapi_pagination import Page
@@ -165,6 +167,13 @@ def patch_sequence(
     )
 
     if body.name is not None:
+        if isinstance(db_sequence, TemplateSequence):
+            assert_template_sequence_name_available(
+                session,
+                workspace_id=workspace_id,
+                name=body.name,
+                exclude_id=db_sequence.id,
+            )
         db_sequence.name = body.name
 
     if body.sequence_type is not None:
@@ -180,7 +189,16 @@ def patch_sequence(
                 )
         db_sequence.sequence_type = body.sequence_type
 
-    session.commit()
+    try:
+        session.commit()
+    except IntegrityError:
+        session.rollback()
+        if body.name is not None and isinstance(db_sequence, TemplateSequence):
+            raise HTTPException(
+                status_code=409,
+                detail=f"Template sequence '{body.name}' already exists in this workspace",
+            ) from None
+        raise
     session.refresh(db_sequence)
     return sequence_ref(db_sequence)
 
diff --git a/packages/opencloning-db/src/opencloning_db/routers/template_sequences.py b/packages/opencloning-db/src/opencloning_db/routers/template_sequences.py
index 7c23151f..b0b75d83 100644
--- a/packages/opencloning-db/src/opencloning_db/routers/template_sequences.py
+++ b/packages/opencloning-db/src/opencloning_db/routers/template_sequences.py
@@ -2,10 +2,11 @@
 
 from typing import Annotated
 
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.exc import IntegrityError
 
 from opencloning_db.apimodels import SequenceRef, TemplateSequenceCreate, sequence_ref
-from opencloning_db.models import TemplateSequence
+from opencloning_db.models import TemplateSequence, assert_template_sequence_name_available
 from opencloning_db.workspace_deps import WorkspaceContext, get_editor_workspace_ctx
 
 router = APIRouter(tags=['template_sequences'])
@@ -16,13 +17,21 @@ def post_template_sequence(
     ctx: Annotated[WorkspaceContext, Depends(get_editor_workspace_ctx)],
     body: TemplateSequenceCreate,
 ):
-    _, session, _ = ctx.destructure()
+    _, session, workspace_id = ctx.destructure()
+    assert_template_sequence_name_available(session, workspace_id=workspace_id, name=body.name)
     template_sequence = TemplateSequence.from_create(
         name=body.name,
         sequence_type=body.sequence_type,
         ctx=ctx,
     )
     session.add(template_sequence)
-    session.commit()
+    try:
+        session.commit()
+    except IntegrityError:
+        session.rollback()
+        raise HTTPException(
+            status_code=409,
+            detail=f"Template sequence '{body.name}' already exists in this workspace",
+        ) from None
     session.refresh(template_sequence)
     return sequence_ref(template_sequence)
diff --git a/packages/opencloning-db/tests/test_template_sequences.py b/packages/opencloning-db/tests/test_template_sequences.py
index bd2d3b31..2d8fc5b7 100644
--- a/packages/opencloning-db/tests/test_template_sequences.py
+++ b/packages/opencloning-db/tests/test_template_sequences.py
@@ -98,6 +98,87 @@ def test_post_template_sequence_persists_template_subtype(template_sequences_cli
     assert stored.name == 'Template Allele'
 
 
+def test_post_template_sequence_duplicate_name_409(template_sequences_client):
+    c = template_sequences_client['client']
+    headers = workspace_headers(template_sequences_client['token_owner_w1'], template_sequences_client['w1'])
+    first = c.post(
+        '/template_sequences',
+        headers=headers,
+        json={'name': 'Shared Template', 'sequence_type': 'allele'},
+    )
+    assert first.status_code == 200
+
+    second = c.post(
+        '/template_sequences',
+        headers=headers,
+        json={'name': 'Shared Template', 'sequence_type': 'plasmid'},
+    )
+    assert second.status_code == 409
+    assert 'already exists' in second.json()['detail']
+
+
+def test_post_template_sequence_duplicate_name_case_insensitive_409(template_sequences_client):
+    c = template_sequences_client['client']
+    headers = workspace_headers(template_sequences_client['token_owner_w1'], template_sequences_client['w1'])
+    first = c.post(
+        '/template_sequences',
+        headers=headers,
+        json={'name': 'Case Template', 'sequence_type': 'allele'},
+    )
+    assert first.status_code == 200
+
+    second = c.post(
+        '/template_sequences',
+        headers=headers,
+        json={'name': 'case template', 'sequence_type': 'allele'},
+    )
+    assert second.status_code == 409
+    assert 'already exists' in second.json()['detail']
+
+
+def test_patch_template_sequence_duplicate_name_409(template_sequences_client):
+    c = template_sequences_client['client']
+    headers = workspace_headers(template_sequences_client['token_owner_w1'], template_sequences_client['w1'])
+    first = c.post(
+        '/template_sequences',
+        headers=headers,
+        json={'name': 'Rename Target', 'sequence_type': 'allele'},
+    )
+    assert first.status_code == 200
+    other = c.post(
+        '/template_sequences',
+        headers=headers,
+        json={'name': 'Other Template', 'sequence_type': 'allele'},
+    )
+    assert other.status_code == 200
+
+    patch = c.patch(
+        f"/sequences/{first.json()['id']}",
+        headers=headers,
+        json={'name': 'other template'},
+    )
+    assert patch.status_code == 409
+    assert 'already exists' in patch.json()['detail']
+
+
+def test_post_template_sequence_same_name_different_workspace_ok(template_sequences_client):
+    c = template_sequences_client['client']
+    w1_headers = workspace_headers(template_sequences_client['token_owner_w1'], template_sequences_client['w1'])
+    w2_headers = workspace_headers(template_sequences_client['token_owner_w2'], template_sequences_client['w2'])
+    w1 = c.post(
+        '/template_sequences',
+        headers=w1_headers,
+        json={'name': 'Cross Workspace', 'sequence_type': 'allele'},
+    )
+    assert w1.status_code == 200
+    w2 = c.post(
+        '/template_sequences',
+        headers=w2_headers,
+        json={'name': 'Cross Workspace', 'sequence_type': 'allele'},
+    )
+    assert w2.status_code == 200
+
+
 def test_change_circularity_rejects_template_sequence(template_sequences_client):
     """Endpoints guarded by require_real_sequence return 404 for template sequences."""
     c = template_sequences_client['client']
diff --git a/uv.lock b/uv.lock
index 304535a5..328cf2da 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1374,7 +1374,7 @@ wheels = [
 
 [[package]]
 name = "opencloning"
-version = "1.6.0"
+version = "1.6.1"
 source = { editable = "packages/opencloning" }
 dependencies = [
     { name = "beautifulsoup4" },
@@ -1425,7 +1425,7 @@ requires-dist = [
 
 [[package]]
 name = "opencloning-cli"
-version = "1.6.0"
+version = "1.6.1"
 source = { editable = "packages/opencloning-cli" }
 dependencies = [
     { name = "opencloning-db" },
@@ -1440,7 +1440,7 @@ requires-dist = [
 
 [[package]]
 name = "opencloning-db"
-version = "1.6.0"
+version = "1.6.1"
 source = { editable = "packages/opencloning-db" }
 dependencies = [
     { name = "boto3" },