diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index b7f346e050f43e011c998a05a11366beec64c6b1..3d084bb1789a1c98b2f5373ae66d7569bbea039d 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -289,7 +289,13 @@ def cache
         end
 
         def dealloc(key)
-          @connection.query "DEALLOCATE #{key}"
+          @connection.query "DEALLOCATE #{key}" if connection_active?
+        end
+
+        def connection_active?
+          @connection.status == PGconn::CONNECTION_OK
+        rescue PGError
+          false
         end
       end
 
diff --git a/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb b/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
index a82c6f67d6604c1dff33e9df79dd36b01385b7c9..f1c4b851269a697d7a2736af5544aa05a7d40e61 100644
--- a/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
@@ -2,6 +2,16 @@
 
 module ActiveRecord::ConnectionAdapters
   class PostgreSQLAdapter < AbstractAdapter
+    class InactivePGconn
+      def query(*args)
+        raise PGError
+      end
+
+      def status
+        PGconn::CONNECTION_BAD
+      end
+    end
+
     class StatementPoolTest < ActiveRecord::TestCase
       def test_cache_is_per_pid
         return skip('must support fork') unless Process.respond_to?(:fork)
@@ -18,6 +28,12 @@ def test_cache_is_per_pid
         Process.waitpid pid
         assert $?.success?, 'process should exit successfully'
       end
+
+      def test_dealloc_does_not_raise_on_inactive_connection
+        cache = StatementPool.new InactivePGconn.new, 10
+        cache['foo'] = 'bar'
+        assert_nothing_raised { cache.clear }
+      end
     end
   end
 end