diff --git a/HISTORY.rst b/HISTORY.rst
index e5b851be22..e0b47b086a 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -8,6 +8,11 @@
   directories.
 * Fixed duplicated FUSE directory removal.
 * Add link and view to show the parsed content of each document page.
+* Add a modelform for adding and editing transformation and perform
+  YAML validation of arguments.
+* Add stricted error checking to the crop transformation.
+* Update compressed files class module to work with Python 3.
+
 
 3.1.4 (2018-10-4)
 =================
diff --git a/mayan/apps/converter/forms.py b/mayan/apps/converter/forms.py
new file mode 100644
index 0000000000..41dd34b4f4
--- /dev/null
+++ b/mayan/apps/converter/forms.py
@@ -0,0 +1,25 @@
+from __future__ import unicode_literals
+
+import yaml
+
+from django import forms
+from django.core.exceptions import ValidationError
+from django.utils.translation import ugettext_lazy as _
+
+from .models import Transformation
+
+
+class TransformationForm(forms.ModelForm):
+    class Meta:
+        fields = ('name', 'arguments', 'order')
+        model = Transformation
+
+    def clean(self):
+        try:
+            yaml.safe_load(self.cleaned_data['arguments'])
+        except yaml.YAMLError:
+            raise ValidationError(
+                _(
+                    '"%s" not a valid entry.'
+                ) % self.cleaned_data['arguments']
+            )
diff --git a/mayan/apps/converter/managers.py b/mayan/apps/converter/managers.py
index 6050a56cd9..484fe45b24 100644
--- a/mayan/apps/converter/managers.py
+++ b/mayan/apps/converter/managers.py
@@ -18,7 +18,7 @@ class TransformationManager(models.Manager):
 
         self.create(
             content_type=content_type, object_id=obj.pk,
-            name=transformation.name, arguments=arguments
+            name=transformation.name, arguments=yaml.safe_dump(arguments)
         )
 
     def copy(self, source, targets):
diff --git a/mayan/apps/converter/transformations.py b/mayan/apps/converter/transformations.py
index deca867239..365f4ae0b7 100644
--- a/mayan/apps/converter/transformations.py
+++ b/mayan/apps/converter/transformations.py
@@ -84,10 +84,25 @@ class TransformationCrop(BaseTransformation):
     def execute_on(self, *args, **kwargs):
         super(TransformationCrop, self).execute_on(*args, **kwargs)
 
-        left = float(self.left or '0')
-        top = float(self.top or '0')
-        right = self.image.size[0] - float(self.right or '0')
-        bottom = self.image.size[1] - float(self.bottom or '0')
+        try:
+            left = int(self.left or '0')
+        except ValueError:
+            left = 0
+
+        try:
+            top = int(self.top or '0')
+        except ValueError:
+            top = 0
+
+        try:
+            right = int(self.right or '0')
+        except ValueError:
+            right = 0
+
+        try:
+            bottom = int(self.bottom or '0')
+        except ValueError:
+            bottom = 0
 
         if left < 0:
             left = 0
@@ -113,6 +128,15 @@ class TransformationCrop(BaseTransformation):
         if bottom > self.image.size[1] - 1:
             bottom = self.image.size[1] - 1
 
+        # Invert right value
+        # Pillow uses left, top, right, bottom to define a viewport
+        # of real coordinates
+        # We invert the right and bottom to define a viewport
+        # that can crop from the right and bottom borders without
+        # having to know the real dimensions of an image
+        right = self.image.size[0] - right
+        bottom = self.image.size[1] - bottom
+
         if left > right:
             left = right - 1
 
diff --git a/mayan/apps/converter/views.py b/mayan/apps/converter/views.py
index ace519c2f7..f9af17a751 100644
--- a/mayan/apps/converter/views.py
+++ b/mayan/apps/converter/views.py
@@ -15,6 +15,7 @@ from common.views import (
     SingleObjectListView
 )
 
+from .forms import TransformationForm
 from .icons import icon_transformation
 from .links import link_transformation_create
 from .models import Transformation
@@ -75,7 +76,7 @@ class TransformationDeleteView(SingleObjectDeleteView):
 
 
 class TransformationCreateView(SingleObjectCreateView):
-    fields = ('name', 'arguments')
+    form_class = TransformationForm
 
     def dispatch(self, request, *args, **kwargs):
         content_type = get_object_or_404(
@@ -133,7 +134,7 @@ class TransformationCreateView(SingleObjectCreateView):
 
 
 class TransformationEditView(SingleObjectEditView):
-    fields = ('name', 'arguments', 'order')
+    form_class = TransformationForm
     model = Transformation
 
     def dispatch(self, request, *args, **kwargs):