diff --git a/config.py b/config.py
index 7d8f310f2..7f347eb3c 100644
--- a/config.py
+++ b/config.py
@@ -6,6 +6,7 @@ import wx
 from logbook import CRITICAL, DEBUG, ERROR, FingersCrossedHandler, INFO, Logger, NestedSetup, NullHandler, \
     StreamHandler, TimedRotatingFileHandler, WARNING
 import hashlib
+from eos.const import Slot
 
 from cryptography.fernet import Fernet
 
@@ -48,11 +49,13 @@ LOGLEVEL_MAP = {
     "debug": DEBUG,
 }
 
-slotColourMap = {1: wx.Colour(250, 235, 204),  # yellow = low slots
-                 2: wx.Colour(188, 215, 241),  # blue   = mid slots
-                 3: wx.Colour(235, 204, 209),  # red    = high slots
-                 4: '',
-                 5: '' }
+slotColourMap = {
+    Slot.LOW: wx.Colour(250, 235, 204),  # yellow = low slots
+    Slot.MED: wx.Colour(188, 215, 241),  # blue   = mid slots
+    Slot.HIGH: wx.Colour(235, 204, 209),  # red    = high slots
+    Slot.RIG: '',
+    Slot.SUBSYSTEM: ''
+}
 
 def getClientSecret():
     return clientHash
diff --git a/eos/const.py b/eos/const.py
new file mode 100644
index 000000000..95dd8a888
--- /dev/null
+++ b/eos/const.py
@@ -0,0 +1,26 @@
+from eos.enum import Enum
+
+
+
+class Slot(Enum):
+    # These are self-explanatory
+    LOW = 1
+    MED = 2
+    HIGH = 3
+    RIG = 4
+    SUBSYSTEM = 5
+    # not a real slot, need for pyfa display rack separation
+    MODE = 6
+    # system effects. They are projected "modules" and pyfa assumes all modules
+    # have a slot. In this case, make one up.
+    SYSTEM = 7
+    # used for citadel services
+    SERVICE = 8
+    # fighter 'slots'. Just easier to put them here...
+    F_LIGHT = 10
+    F_SUPPORT = 11
+    F_HEAVY = 12
+    # fighter 'slots' (for structures)
+    FS_LIGHT = 13
+    FS_SUPPORT = 14
+    FS_HEAVY = 15
diff --git a/eos/gamedata.py b/eos/gamedata.py
index 7c08d6d18..1abb3f69b 100644
--- a/eos/gamedata.py
+++ b/eos/gamedata.py
@@ -240,7 +240,6 @@ class Item(EqBase):
         self.__assistive = None
         self.__overrides = None
         self.__priceObj = None
-        self.__slot = None
 
     @property
     def attributes(self):
@@ -480,21 +479,6 @@ class Item(EqBase):
     def isCharge(self):
         return self.category.name == "Charge"
 
-    effectSlots = { 'loPower'  : 1,
-                    'medPower' : 2,
-                    'hiPower'  : 3,
-                    'rigSlot'  : 4,
-                    'subSystem': 5 }
-    @property
-    def slot(self):
-        if self.__slot is None:
-            self.__slot = 0
-            for effectName in self.effectSlots:
-                if effectName in self.effects:
-                    self.__slot = self.effectSlots[effectName]
-                    break
-        return self.__slot;
-
     def __repr__(self):
         return "Item(ID={}, name={}) at {}".format(
                 self.ID, self.name, hex(id(self))
diff --git a/eos/saveddata/module.py b/eos/saveddata/module.py
index c4c2f0b00..25b15e147 100644
--- a/eos/saveddata/module.py
+++ b/eos/saveddata/module.py
@@ -23,6 +23,7 @@ from logbook import Logger
 from sqlalchemy.orm import reconstructor, validates
 
 import eos.db
+from eos.const import Slot
 from eos.effectHandlerHelpers import HandledCharge, HandledItem
 from eos.enum import Enum
 from eos.modifiedAttributeDict import ChargeAttrShortcut, ItemAttrShortcut, ModifiedAttributeDict
@@ -42,30 +43,6 @@ class State(Enum):
     OVERHEATED = 2
 
 
-class Slot(Enum):
-    # These are self-explanatory
-    LOW = 1
-    MED = 2
-    HIGH = 3
-    RIG = 4
-    SUBSYSTEM = 5
-    # not a real slot, need for pyfa display rack separation
-    MODE = 6
-    # system effects. They are projected "modules" and pyfa assumes all modules
-    # have a slot. In this case, make one up.
-    SYSTEM = 7
-    # used for citadel services
-    SERVICE = 8
-    # fighter 'slots'. Just easier to put them here...
-    F_LIGHT = 10
-    F_SUPPORT = 11
-    F_HEAVY = 12
-    # fighter 'slots' (for structures)
-    FS_LIGHT = 13
-    FS_SUPPORT = 14
-    FS_HEAVY = 15
-
-
 ProjectedMap = {
     State.OVERHEATED: State.ACTIVE,
     State.ACTIVE: State.OFFLINE,
@@ -185,7 +162,7 @@ class Module(HandledItem, HandledCharge, ItemAttrShortcut, ChargeAttrShortcut):
             self.__itemModifiedAttributes.original = self.__item.attributes
             self.__itemModifiedAttributes.overrides = self.__item.overrides
             self.__hardpoint = self.__calculateHardpoint(self.__item)
-            self.__slot = self.__calculateSlot(self.__item)
+            self.__slot = self.calculateSlot(self.__item)
 
             # Instantiate / remove mutators if this is a mutated module
             if self.__baseItem:
@@ -755,7 +732,7 @@ class Module(HandledItem, HandledCharge, ItemAttrShortcut, ChargeAttrShortcut):
         return Hardpoint.NONE
 
     @staticmethod
-    def __calculateSlot(item):
+    def calculateSlot(item):
         effectSlotMap = {
             "rigSlot"    : Slot.RIG,
             "loPower"    : Slot.LOW,
@@ -772,7 +749,7 @@ class Module(HandledItem, HandledCharge, ItemAttrShortcut, ChargeAttrShortcut):
         if item.group.name in Module.SYSTEM_GROUPS:
             return Slot.SYSTEM
 
-        raise ValueError("Passed item does not fit in any known slot")
+        return None
 
     @validates("ID", "itemID", "ammoID")
     def validator(self, key, val):
diff --git a/gui/builtinMarketBrowser/itemView.py b/gui/builtinMarketBrowser/itemView.py
index 7f26a9055..258c8800f 100644
--- a/gui/builtinMarketBrowser/itemView.py
+++ b/gui/builtinMarketBrowser/itemView.py
@@ -1,6 +1,7 @@
 import wx
 from logbook import Logger
 
+from eos.saveddata.module import Module
 import gui.builtinMarketBrowser.pfSearchBox as SBox
 from gui.builtinMarketBrowser.events import ItemSelected, MAX_RECENTLY_USED_MODULES, RECENTLY_USED_MODULES
 from gui.contextMenu import ContextMenu
@@ -271,7 +272,6 @@ class ItemView(Display):
 
     def columnBackground(self, colItem, item):
         if self.sFit.serviceFittingOptions["colorFitBySlot"]:
-            slot = item.slot
-            return slotColourMap.get(slot) or self.GetBackgroundColour()
+            return slotColourMap.get(Module.calculateSlot(item)) or self.GetBackgroundColour()
         else:
             return self.GetBackgroundColour()