diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index b9d7e71c86..099d5ab6cd 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -2,6 +2,7 @@ from __future__ import unicode_literals
 from django.utils.translation import ugettext as _
 from django.db import models
 from django.db.models import Sum
+from django.core.validators import MinValueValidator
 
 from InvenTree.models import InvenTreeTree
 
@@ -35,7 +36,7 @@ class Part(models.Model):
     category = models.ForeignKey(PartCategory, on_delete=models.CASCADE)
 
     # Minimum "allowed" stock level
-    minimum_stock = models.PositiveIntegerField(default=0)
+    minimum_stock = models.PositiveIntegerField(default=0, validators=[MinValueValidator(0)])
 
     # Units of quantity for this part. Default is "pcs"
     units = models.CharField(max_length=20, default="pcs", blank=True)
@@ -112,7 +113,8 @@ class PartParameterTemplate(models.Model):
 
     format = models.PositiveIntegerField(
         default=PARAM_NUMERIC,
-        choices=PARAM_TYPE_CODES.items())
+        choices=PARAM_TYPE_CODES.items(),
+        validators=[MinValueValidator(0)])
 
     def __str__(self):
         return "{name} ({units})".format(
diff --git a/InvenTree/part/views.py b/InvenTree/part/views.py
index a77638c753..d2a1e9f55d 100644
--- a/InvenTree/part/views.py
+++ b/InvenTree/part/views.py
@@ -1,5 +1,4 @@
 from django_filters.rest_framework import FilterSet, DjangoFilterBackend
-from django_filters import NumberFilter
 
 from rest_framework import generics, permissions
 
diff --git a/InvenTree/project/models.py b/InvenTree/project/models.py
index 8038184215..99228deb22 100644
--- a/InvenTree/project/models.py
+++ b/InvenTree/project/models.py
@@ -5,6 +5,7 @@ from django.db import models
 
 from InvenTree.models import InvenTreeTree
 from part.models import Part
+from django.core.validators import MinValueValidator
 
 
 class ProjectCategory(InvenTreeTree):
@@ -46,7 +47,7 @@ class ProjectPart(models.Model):
 
     part = models.ForeignKey(Part, on_delete=models.CASCADE)
     project = models.ForeignKey(Project, on_delete=models.CASCADE)
-    quantity = models.PositiveIntegerField(default=1)
+    quantity = models.PositiveIntegerField(default=1, validators=[MinValueValidator(0)])
 
     class Meta:
         unique_together = ('part', 'project')
@@ -66,7 +67,8 @@ class ProjectPart(models.Model):
     overage = models.FloatField(default=0)
     overage_type = models.PositiveIntegerField(
         default=OVERAGE_ABSOLUTE,
-        choices=OVARAGE_CODES.items())
+        choices=OVARAGE_CODES.items(),
+        validators=[MinValueValidator(0)])
     """
 
     # Set if the part is generated by the project,
@@ -89,6 +91,6 @@ class ProjectRun(models.Model):
     """
 
     project = models.ForeignKey(Project, on_delete=models.CASCADE)
-    quantity = models.PositiveIntegerField(default=1)
+    quantity = models.PositiveIntegerField(default=1, validators=[MinValueValidator(0)])
 
     run_date = models.DateField(auto_now_add=True)
diff --git a/InvenTree/stock/models.py b/InvenTree/stock/models.py
index 703bd3b9fe..0c847e80d5 100644
--- a/InvenTree/stock/models.py
+++ b/InvenTree/stock/models.py
@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 from django.utils.translation import ugettext as _
 from django.db import models
+from django.core.validators import MinValueValidator
 
 from supplier.models import SupplierPart
 from part.models import Part
@@ -21,7 +22,7 @@ class StockItem(models.Model):
     part = models.ForeignKey(Part, on_delete=models.CASCADE, related_name='locations')
     supplier_part = models.ForeignKey(SupplierPart, blank=True, null=True, on_delete=models.SET_NULL)
     location = models.ForeignKey(StockLocation, on_delete=models.CASCADE)
-    quantity = models.PositiveIntegerField()
+    quantity = models.PositiveIntegerField(validators=[MinValueValidator(0)])
     updated = models.DateField(auto_now=True)
 
     # last time the stock was checked / counted
@@ -50,7 +51,8 @@ class StockItem(models.Model):
 
     status = models.PositiveIntegerField(
         default=ITEM_IN_STOCK,
-        choices=ITEM_STATUS_CODES.items())
+        choices=ITEM_STATUS_CODES.items(),
+        validators=[MinValueValidator(0)])
 
     notes = models.CharField(max_length=100, blank=True)
 
diff --git a/InvenTree/supplier/models.py b/InvenTree/supplier/models.py
index 9f5067caf8..13393bb4ad 100644
--- a/InvenTree/supplier/models.py
+++ b/InvenTree/supplier/models.py
@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 from django.db import models
+from django.core.validators import MinValueValidator
 
 from InvenTree.models import Company
 from part.models import Part
@@ -54,10 +55,10 @@ class SupplierPart(models.Model):
     packaging = models.CharField(max_length=50, blank=True)
 
     # multiple that the part is provided in
-    multiple = models.PositiveIntegerField(default=1)
+    multiple = models.PositiveIntegerField(default=1, validators=[MinValueValidator(0)])
 
     # Mimumum number required to order
-    minimum = models.PositiveIntegerField(default=1)
+    minimum = models.PositiveIntegerField(default=1, validators=[MinValueValidator(0)])
 
     # lead time for parts that cannot be delivered immediately
     lead_time = models.DurationField(blank=True, null=True)
@@ -75,7 +76,7 @@ class SupplierPriceBreak(models.Model):
     """
 
     part = models.ForeignKey(SupplierPart, on_delete=models.CASCADE, related_name='price_breaks')
-    quantity = models.PositiveIntegerField()
+    quantity = models.PositiveIntegerField(validators=[MinValueValidator(0)])
     cost = models.DecimalField(max_digits=10, decimal_places=3)
 
     class Meta:
diff --git a/InvenTree/supplier/views.py b/InvenTree/supplier/views.py
index aed416f56b..8f9b43e03a 100644
--- a/InvenTree/supplier/views.py
+++ b/InvenTree/supplier/views.py
@@ -1,5 +1,4 @@
 from django_filters.rest_framework import FilterSet, DjangoFilterBackend
-from django_filters import NumberFilter
 
 from rest_framework import generics, permissions