diff --git a/pillar/api/custom_field_validation.py b/pillar/api/custom_field_validation.py
index 1decfb85..5e8396fd 100644
--- a/pillar/api/custom_field_validation.py
+++ b/pillar/api/custom_field_validation.py
@@ -1,8 +1,7 @@
+from datetime import datetime
 import logging
 
 from bson import ObjectId, tz_util
-from datetime import datetime
-import cerberus.errors
 from eve.io.mongo import Validator
 from flask import current_app
 
@@ -12,6 +11,24 @@ log = logging.getLogger(__name__)
 
 
 class ValidateCustomFields(Validator):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        # Will be reference to the actual document being validated, so that we can
+        # modify it during validation.
+        self.__real_document = None
+
+    def validate(self, document, *args, **kwargs):
+        # Keep a reference to the actual document, because Cerberus validates copies.
+        self.__real_document = document
+        return super().validate(document, *args, **kwargs)
+
+    def _get_child_validator(self, *args, **kwargs):
+        child = super()._get_child_validator(*args, **kwargs)
+        # Pass along our reference to the actual document.
+        child.__real_document = self.__real_document
+        return child
+
     # TODO: split this into a convert_property(property, schema) and call that from this function.
     def convert_properties(self, properties, node_schema):
         """Converts datetime strings and ObjectId strings to actual Python objects."""
@@ -160,26 +177,25 @@ class ValidateCustomFields(Validator):
         if ip.prefixlen() == 0:
             self._error(field_name, 'Zero-length prefix is not allowed')
 
-    # def _validate_coerce(self, coerce, field: str, value):
-    #     """Override Cerberus' _validate_coerce method for richer features.
-    #
-    #     This now supports named coercion functions (available in Cerberus 1.0+)
-    #     and passes the field name to coercion functions as well.
-    #     """
-    #     if isinstance(coerce, str):
-    #         coerce = getattr(self, f'_normalize_coerce_{coerce}')
-    #
-    #     try:
-    #         return coerce(field, value)
-    #     except (TypeError, ValueError):
-    #         self._error(field, cerberus.errors.ERROR_COERCION_FAILED.format(field))
-
     def _validator_markdown(self, field, value):
-        """This is a placeholder.
-
-        Markdown is actually processed in a hook
+        """Convert MarkDown.
         """
-        return value
+        # Find this field inside the original document
+        my_subdoc = self._subdoc_in_real_document()
+
+        save_to = pillar.markdown.cache_field_name(field)
+        html = pillar.markdown.markdown(value)
+        my_subdoc[save_to] = html
+
+    def _subdoc_in_real_document(self):
+        """Return a reference to the current sub-document inside the real document.
+
+        This allows modification of the document being validated.
+        """
+        my_subdoc = self.__real_document
+        for item in self.document_path:
+            my_subdoc = my_subdoc[item]
+        return my_subdoc
 
 
 if __name__ == '__main__':
diff --git a/tests/test_api/test_cerberus.py b/tests/test_api/test_cerberus.py
index d0079229..01174f48 100644
--- a/tests/test_api/test_cerberus.py
+++ b/tests/test_api/test_cerberus.py
@@ -36,7 +36,7 @@ class CerberusCanaryTest(unittest.TestCase):
         self._canary_test(validator)
 
 
-class ValidationTest(AbstractPillarTest):
+class AbstractValidationTest(AbstractPillarTest):
     def setUp(self):
         super().setUp()
 
@@ -57,7 +57,7 @@ class ValidationTest(AbstractPillarTest):
         self.assertFalse(is_valid)
 
 
-class ProjectValidationTest(ValidationTest):
+class ProjectValidationTest(AbstractValidationTest):
 
     def test_empty(self):
         from pillar.api.eve_settings import projects_schema
@@ -93,7 +93,7 @@ class ProjectValidationTest(ValidationTest):
         self.assertValid(project, projects_schema)
 
 
-class NodeValidationTest(ValidationTest):
+class NodeValidationTest(AbstractValidationTest):
     def setUp(self):
         super().setUp()
         self.pid, self.project = self.ensure_project_exists()
@@ -172,8 +172,8 @@ class NodeValidationTest(ValidationTest):
         self.assertValid(comment, nodes_schema)
 
 
-class IPRangeValidatorTest(ValidationTest):
-    schema = {'iprange': {'type': 'string', 'required': True, 'validator': 'iprange'}}
+class AbstractSchemaValidationTest(AbstractValidationTest):
+    schema = {}
 
     def assertValid(self, document, schema=None):
         return super().assertValid(document, schema or self.schema)
@@ -181,6 +181,10 @@ class IPRangeValidatorTest(ValidationTest):
     def assertInvalid(self, document, schema=None):
         return super().assertInvalid(document, schema or self.schema)
 
+
+class IPRangeValidatorTest(AbstractSchemaValidationTest):
+    schema = {'iprange': {'type': 'string', 'required': True, 'validator': 'iprange'}}
+
     def test_ipv6(self):
         self.assertValid({'iprange': '2a03:b0c0:0:1010::8fe:6ef1'})
         self.assertValid({'iprange': '0:0:0:0:0:ffff:102:304'})
@@ -207,3 +211,34 @@ class IPRangeValidatorTest(ValidationTest):
         err = self.validator._errors[0]
         self.assertEquals(('iprange', ), err.document_path)
         self.assertEquals(('Zero-length prefix is not allowed',), err.info)
+
+
+class MarkdownValidatorTest(AbstractSchemaValidationTest):
+    schema = {'subdoc': {
+        'type': 'list',
+        'schema': {
+            'type': 'dict',
+            'schema': {
+                'content': {'type': 'string', 'required': True, 'validator': 'markdown'},
+                '_content_html': {'type': 'string'},
+                'descr': {'type': 'string', 'required': True, 'validator': 'markdown'},
+                '_descr_html': {'type': 'string'},
+            }
+        },
+    }}
+
+    def test_in_subdoc(self):
+        doc = {'subdoc': [{
+            'content': '# Header\n\nSome text',
+            'descr': 'je moeder'
+        }]}
+        self.validator.validate(doc, self.schema, normalize=True)
+
+        expect = {'subdoc': [{
+            'content': '# Header\n\nSome text',
+            '_content_html': '<h1>Header</h1>\n<p>Some text</p>\n',
+            'descr': 'je moeder',
+            '_descr_html': '<p>je moeder</p>\n',
+        }]}
+
+        self.assertEqual(expect, doc)