diff --git a/starpunk/micropub.py b/starpunk/micropub.py
index 2bb05c0..0e2a4e8 100644
--- a/starpunk/micropub.py
+++ b/starpunk/micropub.py
@@ -287,6 +287,17 @@ def handle_create(data: dict, token_info: dict):
             "insufficient_scope", "Token lacks create scope", status_code=403
         )
 
+    # Extract mp-slug BEFORE normalizing properties (it's not a property!)
+    # mp-slug is a Micropub server extension parameter that gets filtered during normalization
+    custom_slug = None
+    if isinstance(data, dict) and 'mp-slug' in data:
+        # Handle both form-encoded (list) and JSON (could be string or list)
+        slug_value = data.get('mp-slug')
+        if isinstance(slug_value, list) and slug_value:
+            custom_slug = slug_value[0]
+        elif isinstance(slug_value, str):
+            custom_slug = slug_value
+
     # Normalize and extract properties
     try:
         properties = normalize_properties(data)
@@ -295,14 +306,6 @@ def handle_create(data: dict, token_info: dict):
         tags = extract_tags(properties)
         published_date = extract_published_date(properties)
 
-        # Extract custom slug if provided (Micropub extension)
-        custom_slug = None
-        if 'mp-slug' in properties:
-            # mp-slug is an array in Micropub format
-            slug_values = properties.get('mp-slug', [])
-            if slug_values and len(slug_values) > 0:
-                custom_slug = slug_values[0]
-
     except MicropubValidationError as e:
         raise e
     except Exception as e:
diff --git a/tests/test_micropub.py b/tests/test_micropub.py
index 45f712b..7cf482c 100644
--- a/tests/test_micropub.py
+++ b/tests/test_micropub.py
@@ -188,6 +188,64 @@ def test_micropub_create_with_categories(client, app, mock_valid_token):
         assert 'Location' in response.headers
 
 
+def test_micropub_create_with_custom_slug_form(client, app, mock_valid_token):
+    """Test creating a note with custom slug via form-encoded request"""
+    with patch('starpunk.routes.micropub.verify_external_token', mock_valid_token):
+        response = client.post(
+            '/micropub',
+            data={
+                'h': 'entry',
+                'content': 'This is a test for custom slugs',
+                'mp-slug': 'my-custom-slug'
+            },
+            headers={'Authorization': 'Bearer valid_token'}
+        )
+
+        assert response.status_code == 201
+        assert 'Location' in response.headers
+
+        # Verify the custom slug was used
+        location = response.headers['Location']
+        assert location.endswith('/notes/my-custom-slug')
+
+        # Verify note exists with the custom slug
+        with app.app_context():
+            note = get_note('my-custom-slug')
+            assert note is not None
+            assert note.slug == 'my-custom-slug'
+            assert note.content == 'This is a test for custom slugs'
+
+
+def test_micropub_create_with_custom_slug_json(client, app, mock_valid_token):
+    """Test creating a note with custom slug via JSON request"""
+    with patch('starpunk.routes.micropub.verify_external_token', mock_valid_token):
+        response = client.post(
+            '/micropub',
+            json={
+                'type': ['h-entry'],
+                'properties': {
+                    'content': ['JSON test with custom slug']
+                },
+                'mp-slug': 'json-custom-slug'
+            },
+            headers={'Authorization': 'Bearer valid_token'}
+        )
+
+        assert response.status_code == 201
+        assert 'Location' in response.headers
+
+        # Verify the custom slug was used
+        location = response.headers['Location']
+        assert location.endswith('/notes/json-custom-slug')
+
+        # Verify note exists with the custom slug
+        with app.app_context():
+            note = get_note('json-custom-slug')
+            assert note is not None
+            assert note.slug == 'json-custom-slug'
+            assert note.content == 'JSON test with custom slug'
+
+
 # Query Tests