diff --git a/setup.py b/setup.py
index 94d7a11..d9ce238 100755
--- a/setup.py
+++ b/setup.py
@@ -3,7 +3,7 @@
 
 setup(
     name="Tornado-MySQL",
-    version="0.5.1",
+    version="0.5.2",
     url='https://github.com/PyMySQL/Tornado-MySQL',
     author='INADA Naoki',
     author_email='songofacandy@gmail.com',
diff --git a/tornado_mysql/pools.py b/tornado_mysql/pools.py
index bb3e721..5fe5c44 100644
--- a/tornado_mysql/pools.py
+++ b/tornado_mysql/pools.py
@@ -72,13 +72,19 @@ def _get_conn(self):
         if self.max_open == 0 or self._opened_conns < self.max_open:
             self._opened_conns += 1
             log.debug("Creating new connection: %s", self.stat())
-            return connect(**self.connect_kwargs)
+            fut = connect(**self.connect_kwargs)
+            fut.add_done_callback(self._on_connect)  # self._opened_conns -=1 on exception
+            return fut
 
         # Wait to other connection is released.
         fut = Future()
         self._waitings.append(fut)
         return fut
 
+    def _on_connect(self, fut):
+        if fut.exception():
+            self._opened_conns -= 1
+
     def _put_conn(self, conn):
         if (len(self._free_conn) < self.max_idle and
                 self.io_loop.time() - conn.connected_time < self.max_recycle_sec):