diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index e3c7344f59dad896fa4ea04ab5ef028f800b0a9a..0560f6394953eb21d0937e842a00bbfa3df22f23 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -102,6 +102,8 @@ def primary_key=(value)
           @original_primary_key = @primary_key if defined?(@primary_key)
           @primary_key          = value && value.to_s
           @quoted_primary_key   = nil
+
+          connection.schema_cache.primary_keys[table_name] = @primary_key if connected?
         end
 
         def set_primary_key(value = nil, &block) #:nodoc:
diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index 8d248c3f9fb44b63e7be8540f1c1c9723070f5a5..a02dcb9e1c6b1f479372d3dd4c358f41bc75440c 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -148,6 +148,16 @@ def test_quoted_primary_key_after_set_primary_key
     k.primary_key = "foo"
     assert_equal k.connection.quote_column_name("foo"), k.quoted_primary_key
   end
+
+  def test_set_primary_key_sets_schema_cache
+    klass = Class.new(ActiveRecord::Base)
+    klass.table_name = 'fuuuuuu'
+    klass.connection.create_table(:fuuuuuu, :id => false) { |t| t.integer :omg }
+    klass.primary_key = 'omg'
+    assert klass.connection.schema_cache.columns_hash['fuuuuuu']['omg'].primary
+  ensure
+    klass.connection.drop_table(:fuuuuuu) if klass.table_exists?
+  end
 end
 
 class PrimaryKeyWithNoConnectionTest < ActiveRecord::TestCase