diff --git a/lib/couchrest/model/associations.rb b/lib/couchrest/model/associations.rb
index 0f83f3e..889ff5c 100644
--- a/lib/couchrest/model/associations.rb
+++ b/lib/couchrest/model/associations.rb
@@ -171,27 +171,32 @@ module CouchRest
       (array ||= []).compact!
       casted_by[property.to_s] = [] # replace the original array!
       array.compact.each do |obj|
+        check_obj(obj)
         casted_by[property.to_s] << obj.id
       end
       super(array)
     end
     
     def << obj
+      check_obj(obj)
       casted_by[property.to_s] << obj.id
       super(obj)
     end
     
     def push(obj)
+      check_obj(obj)
       casted_by[property.to_s].push obj.id
       super(obj)
     end
     
     def unshift(obj)
+      check_obj(obj)
       casted_by[property.to_s].unshift obj.id
       super(obj)
     end
 
     def []= index, obj
+      check_obj(obj)
       casted_by[property.to_s][index] = obj.id
       super(index, obj)
     end
@@ -205,6 +210,13 @@ module CouchRest
       casted_by[property.to_s].shift
       super
     end
+
+    protected
+
+    def check_obj(obj)
+      raise "Object cannot be added to #{casted_by.class.to_s}##{property.to_s} collection unless saved" if obj.new?
+    end
+
   end
 
 
diff --git a/spec/couchrest/assocations_spec.rb b/spec/couchrest/assocations_spec.rb
index 21ad658..deef3cb 100644
--- a/spec/couchrest/assocations_spec.rb
+++ b/spec/couchrest/assocations_spec.rb
@@ -178,16 +178,19 @@ describe "Assocations" do
         @invoice.entry_ids.first.should eql(@entries[1].id)
       end
       
-      it "should save all entries when invoice is saved" do
+      it "should raise error when adding un-persisted entries" do
         SaleEntry.find_by_description('test entry').should be_nil
         entry = SaleEntry.new(:description => 'test entry', :price => 500)
-        @invoice.entries << entry
-        @invoice.save.should be_true
-        SaleEntry.find_by_description('test entry').should_not be_nil
+        lambda {
+          @invoice.entries << entry
+        }.should raise_error
+        # In the future maybe?
+        # @invoice.save.should be_true
+        # SaleEntry.find_by_description('test entry').should_not be_nil
       end
 
     end
 
   end
 
-end
\ No newline at end of file
+end