diff --git a/eos b/eos
index be10e9956..5b7f8eaf7 160000
--- a/eos
+++ b/eos
@@ -1 +1 @@
-Subproject commit be10e9956ce476fb33f121fcca0e69a1bca02104
+Subproject commit 5b7f8eaf715cfaa9a835a4057ad6c0671d2ecdc2
diff --git a/service/fit.py b/service/fit.py
index b5f1852e8..fc9cbf4a0 100644
--- a/service/fit.py
+++ b/service/fit.py
@@ -168,7 +168,11 @@ class Fit(object):
         except ValueError:
             return False
 
+        if m.item.category.name == "Subsystem":
+            fit.modules.freeSlot(m.getModifiedItemAttr("subSystemSlot"))
+
         if m.fits(fit):
+
             numSlots = len(fit.modules)
             fit.modules.append(m)
             if m.isValidState(State.ACTIVE):