diff --git a/backend/alembic/versions/0003_add_gltf_asset_type.py b/backend/alembic/versions/0003_add_gltf_asset_type.py
new file mode 100644
index 0000000..449ac6f
--- /dev/null
+++ b/backend/alembic/versions/0003_add_gltf_asset_type.py
@@ -0,0 +1,36 @@
+"""add model_gltf value to asset_type enum
+
+Revision ID: 0003_add_gltf_asset_type
+Revises: 0002_add_date_of_birth_to_users
+Create Date: 2025-06-15 00:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "0003_add_gltf_asset_type"
+down_revision: Union[str, None] = "0002_add_date_of_birth_to_users"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Add the 'model_gltf' value to the asset_type enum."""
+    # IF NOT EXISTS is supported on PostgreSQL 12+; the project targets
+    # PostgreSQL 16. Adding an enum value and using it in the same
+    # transaction is restricted until commit, but this migration only adds
+    # the value so it is safe inside Alembic's transaction.
+    op.execute("ALTER TYPE asset_type ADD VALUE IF NOT EXISTS 'model_gltf'")
+
+
+def downgrade() -> None:
+    """Remove the 'model_gltf' value from the asset_type enum.
+
+    PostgreSQL does not support dropping an enum value without table scans;
+    this is intentionally a no-op to keep downgrades safe. Re-creating the
+    enum or deleting rows that use this value would be a destructive action
+    better performed manually if ever needed.
+    """
+    pass
diff --git a/backend/app/routers/assets.py b/backend/app/routers/assets.py
index 7d68b56..01c5845 100644
--- a/backend/app/routers/assets.py
+++ b/backend/app/routers/assets.py
@@ -73,7 +73,7 @@ def _validate_gltf_json(content: bytes) -> dict:
     """
     try:
         data = json.loads(content)
-    except json.JSONDecodeError as e:
+    except (json.JSONDecodeError, UnicodeDecodeError) as e:
         raise ValueError(f"Invalid JSON in .gltf file: {e}")
 
     if not isinstance(data, dict):
@@ -105,18 +105,18 @@ def _validate_glb(content: bytes) -> dict:
 
     # Check magic bytes: must start with b'glTF'
     magic = content[:4]
-    if magic != b'glTF':
+    if magic != b"glTF":
         raise ValueError(
             f"Invalid glb magic bytes: expected b'glTF', got {magic!r}"
         )
 
     # Version check (we support version 2)
-    version = int.from_bytes(content[4:8], byteorder='little')
+    version = int.from_bytes(content[4:8], byteorder="little")
     if version != 2:
         raise ValueError(f"Unsupported glTF version: {version} (expected 2)")
 
     # Total length check
-    total_length = int.from_bytes(content[8:12], byteorder='little')
+    total_length = int.from_bytes(content[8:12], byteorder="little")
     if total_length != len(content):
         raise ValueError(
             f"glb total length mismatch: header says {total_length}, "
@@ -132,17 +132,17 @@ def _validate_glb(content: bytes) -> dict:
         if offset + 8 > len(content):
             raise ValueError("Incomplete chunk header in glb file")
 
-        chunk_length = int.from_bytes(content[offset:offset+4], byteorder='little')
-        chunk_type = content[offset+4:offset+8]
+        chunk_length = int.from_bytes(content[offset:offset + 4], byteorder="little")
+        chunk_type = content[offset + 4:offset + 8]
 
         if chunk_length + 8 > len(content) - offset:
             raise ValueError("Chunk extends beyond file end")
 
-        if chunk_type == b'JSON':
-            json_chunk_data = content[offset+8:offset+8+chunk_length]
+        if chunk_type == b"JSON":
+            json_chunk_data = content[offset + 8:offset + 8 + chunk_length]
             # JSON chunk may have padding
             break
-        elif chunk_type == b'BIN':
+        elif chunk_type == b"BIN":
             # Skip binary chunk
             offset += 8 + chunk_length
             continue
@@ -156,7 +156,7 @@ def _validate_glb(content: bytes) -> dict:
 
     try:
         data = json.loads(json_chunk_data)
-    except json.JSONDecodeError as e:
+    except (json.JSONDecodeError, UnicodeDecodeError) as e:
         raise ValueError(f"Invalid JSON in glb chunk: {e}")
 
     if not isinstance(data, dict):
@@ -442,10 +442,13 @@ async def import_gltf(
     await db.commit()
     await db.refresh(asset)
 
-    # Sanitize filename for storage
-    safe_filename = _sanitize_filename(filename)
+    # Sanitize filename for storage.
+    # The original extension was validated above, so we keep exactly one
+    # extension after the sanitized stem.
+    original_stem = Path(filename).stem
+    safe_stem = _sanitize_filename(original_stem)
     extension = ".gltf" if lower_filename.endswith(".gltf") else ".glb"
-    stored_name = f"{asset.id}_{safe_filename}{extension}"
+    stored_name = f"{asset.id}_{safe_stem}{extension}"
 
     # Write the file to the upload directory
     upload_dir = Path(settings.UPLOAD_DIR)