diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5bdf5e32b..d27c136a3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -31,6 +31,7 @@ details about the cause of the failure
 -    Fix non-delegate types incorrectly appearing as callable.
 -    Indexers can now be used with interface objects
 -    Fixed a bug where indexers could not be used if they were inherited
+-    Made it possible to use `__len__` also on `ICollection<>` interface objects
 
 ## [2.5.0][] - 2020-06-14
 
diff --git a/src/runtime/slots/mp_length.cs b/src/runtime/slots/mp_length.cs
index 42448a2e9..a13c7b6f8 100644
--- a/src/runtime/slots/mp_length.cs
+++ b/src/runtime/slots/mp_length.cs
@@ -26,7 +26,7 @@ public static MethodInfo Method
             }
         }
 
-        public static bool CanAssgin(Type clrType)
+        public static bool CanAssign(Type clrType)
         {
             if (typeof(ICollection).IsAssignableFrom(clrType))
             {
@@ -36,6 +36,10 @@ public static bool CanAssgin(Type clrType)
             {
                 return true;
             }
+            if (clrType.IsInterface && clrType.IsGenericType && clrType.GetGenericTypeDefinition() == typeof(ICollection<>))
+            {
+                return true;
+            }
             return false;
         }
 
diff --git a/src/runtime/typemanager.cs b/src/runtime/typemanager.cs
index c00247ca4..78c34a027 100644
--- a/src/runtime/typemanager.cs
+++ b/src/runtime/typemanager.cs
@@ -225,7 +225,7 @@ internal static IntPtr CreateType(ManagedType impl, Type clrType)
             InitializeSlots(type, impl.GetType(), slotsHolder);
 
             if (Marshal.ReadIntPtr(type, TypeOffset.mp_length) == IntPtr.Zero
-                && mp_length_slot.CanAssgin(clrType))
+                && mp_length_slot.CanAssign(clrType))
             {
                 InitializeSlot(type, TypeOffset.mp_length, mp_length_slot.Method, slotsHolder);
             }
diff --git a/src/tests/test_mp_length.py b/src/tests/test_mp_length.py
index c96ac77d1..e86fff288 100644
--- a/src/tests/test_mp_length.py
+++ b/src/tests/test_mp_length.py
@@ -47,3 +47,17 @@ def test_custom_generic_collection_explicit___len__():
     s.Add(1)
     s.Add(10)
     assert len(s) == 2
+
+def test_len_through_interface_generic():
+    """Test __len__ for ICollection<T>"""
+    import System.Collections.Generic
+    l = System.Collections.Generic.List[int]()
+    coll = System.Collections.Generic.ICollection[int](l)
+    assert len(coll) == 0
+
+def test_len_through_interface():
+    """Test __len__ for ICollection"""
+    import System.Collections
+    l = System.Collections.ArrayList()
+    coll = System.Collections.ICollection(l)
+    assert len(coll) == 0