change.diff

diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index 8272a55..e8083a5 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -46,8 +46,9 @@ module ActiveRecord
         def update_counters(record)
           with_cache_name do |name|
             return unless different_target? record
-            record.class.increment_counter(name, record.id)
-            decrement_counter name
+            expected = record.read_attribute name
+            record.class.increment_counter(name, record.id, expected)
+            decrement_counter record, name
           end
         end
 
@@ -55,9 +56,10 @@ module ActiveRecord
           with_cache_name { |name| decrement_counter name }
         end
 
-        def decrement_counter counter_cache_name
+        def decrement_counter record, counter_cache_name
           if foreign_key_present?
-            klass.decrement_counter(counter_cache_name, target_id)
+            expected = record.read_attribute counter_cache_name
+            klass.decrement_counter(counter_cache_name, target_id, expected)
           end
         end
 
diff --git a/activerecord/lib/active_record/associations/builder/belongs_to.rb b/activerecord/lib/active_record/associations/builder/belongs_to.rb
index 5ccaa55..68b7570 100644
--- a/activerecord/lib/active_record/associations/builder/belongs_to.rb
+++ b/activerecord/lib/active_record/associations/builder/belongs_to.rb
@@ -32,7 +32,8 @@ module ActiveRecord::Associations::Builder
         def belongs_to_counter_cache_after_create(reflection)
           if record = send(reflection.name)
             cache_column = reflection.counter_cache_column
-            record.class.increment_counter(cache_column, record.id)
+            expected = record.read_attribute cache_column
+            record.class.increment_counter(cache_column, record.id, expected)
             @_after_create_counter_called = true
           end
         end
@@ -43,7 +44,8 @@ module ActiveRecord::Associations::Builder
             record = send reflection.name
             if record && !self.destroyed?
               cache_column = reflection.counter_cache_column
-              record.class.decrement_counter(cache_column, record.id)
+              expected = record.read_attribute cache_column
+              record.class.decrement_counter(cache_column, record.id, expected)
             end
           end
         end
diff --git a/activerecord/lib/active_record/counter_cache.rb b/activerecord/lib/active_record/counter_cache.rb
index dcbdf75..5277a00 100644
--- a/activerecord/lib/active_record/counter_cache.rb
+++ b/activerecord/lib/active_record/counter_cache.rb
@@ -70,14 +70,16 @@ module ActiveRecord
       #   # UPDATE posts
       #   #    SET comment_count = COALESCE(comment_count, 0) + 1
       #   #  WHERE id IN (10, 15)
-      def update_counters(id, counters)
+      def update_counters(id, expected, counters)
+        scope = unscoped
         updates = counters.map do |counter_name, value|
           operator = value < 0 ? '-' : '+'
           quoted_column = connection.quote_column_name(counter_name)
+          scope = scope.where(counter_name => expected)
           "#{quoted_column} = COALESCE(#{quoted_column}, 0) #{operator} #{value.abs}"
         end
 
-        unscoped.where(primary_key => id).update_all updates.join(', ')
+        scope.where(primary_key => id).update_all updates.join(', ')
       end
 
       # Increment a numeric field by one, via a direct SQL update.
@@ -96,8 +98,8 @@ module ActiveRecord
       #
       #   # Increment the post_count column for the record with an id of 5
       #   DiscussionBoard.increment_counter(:post_count, 5)
-      def increment_counter(counter_name, id)
-        update_counters(id, counter_name => 1)
+      def increment_counter(counter_name, id, expected)
+        update_counters(id, expected, counter_name => 1)
       end
 
       # Decrement a numeric field by one, via a direct SQL update.
@@ -114,8 +116,8 @@ module ActiveRecord
       #
       #   # Decrement the post_count column for the record with an id of 5
       #   DiscussionBoard.decrement_counter(:post_count, 5)
-      def decrement_counter(counter_name, id)
-        update_counters(id, counter_name => -1)
+      def decrement_counter(counter_name, id, expected)
+        update_counters(id, expected, counter_name => -1)
       end
     end
   end
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index 4d63b04..a2d211f 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -164,7 +164,7 @@ module ActiveRecord
 
         # Make sure the lock version column gets updated when counters are
         # updated.
-        def update_counters(id, counters)
+        def update_counters(id, counters, expected)
           counters = counters.merge(locking_column => 1) if locking_enabled?
           super
         end