diff --git a/system/libraries/Session/drivers/Session_database_driver.php b/system/libraries/Session/drivers/Session_database_driver.php
index 6a7282b..2f52412 100644
--- a/system/libraries/Session/drivers/Session_database_driver.php
+++ b/system/libraries/Session/drivers/Session_database_driver.php
@@ -208,8 +208,12 @@
 		// Prevent previous QB calls from messing with our queries
 		$this->_db->reset_query();
 
+		if ($this->_lock === FALSE)
+		{
+			return $this->_fail();
+		}
 		// Was the ID regenerated?
-		if ($session_id !== $this->_session_id)
+		elseif ($session_id !== $this->_session_id)
 		{
 			if ( ! $this->_release_lock() OR ! $this->_get_lock($session_id))
 			{
@@ -219,10 +223,6 @@
 			$this->_row_exists = FALSE;
 			$this->_session_id = $session_id;
 		}
-		elseif ($this->_lock === FALSE)
-		{
-			return $this->_fail();
-		}
 
 		if ($this->_row_exists === FALSE)
 		{
diff --git a/system/libraries/Session/drivers/Session_memcached_driver.php b/system/libraries/Session/drivers/Session_memcached_driver.php
index 99b4d1b..eb1dcd3 100644
--- a/system/libraries/Session/drivers/Session_memcached_driver.php
+++ b/system/libraries/Session/drivers/Session_memcached_driver.php
@@ -186,7 +186,7 @@
 	 */
 	public function write($session_id, $session_data)
 	{
-		if ( ! isset($this->_memcached))
+		if ( ! isset($this->_memcached, $this->_lock_key))
 		{
 			return $this->_fail();
 		}
@@ -202,28 +202,25 @@
 			$this->_session_id = $session_id;
 		}
 
-		if (isset($this->_lock_key))
+		$key = $this->_key_prefix.$session_id;
+
+		$this->_memcached->replace($this->_lock_key, time(), 300);
+		if ($this->_fingerprint !== ($fingerprint = md5($session_data)))
 		{
-			$key = $this->_key_prefix.$session_id;
-
-			$this->_memcached->replace($this->_lock_key, time(), 300);
-			if ($this->_fingerprint !== ($fingerprint = md5($session_data)))
+			if ($this->_memcached->set($key, $session_data, $this->_config['expiration']))
 			{
-				if ($this->_memcached->set($key, $session_data, $this->_config['expiration']))
-				{
-					$this->_fingerprint = $fingerprint;
-					return $this->_success;
-				}
-
-				return $this->_fail();
-			}
-			elseif (
-				$this->_memcached->touch($key, $this->_config['expiration'])
-				OR ($this->_memcached->getResultCode() === Memcached::RES_NOTFOUND && $this->_memcached->set($key, $session_data, $this->_config['expiration']))
-			)
-			{
+				$this->_fingerprint = $fingerprint;
 				return $this->_success;
 			}
+
+			return $this->_fail();
+		}
+		elseif (
+			$this->_memcached->touch($key, $this->_config['expiration'])
+			OR ($this->_memcached->getResultCode() === Memcached::RES_NOTFOUND && $this->_memcached->set($key, $session_data, $this->_config['expiration']))
+		)
+		{
+			return $this->_success;
 		}
 
 		return $this->_fail();
@@ -375,4 +372,4 @@
 
 		return TRUE;
 	}
-}
\ No newline at end of file
+}
diff --git a/system/libraries/Session/drivers/Session_redis_driver.php b/system/libraries/Session/drivers/Session_redis_driver.php
index 8db74c0..a780100 100644
--- a/system/libraries/Session/drivers/Session_redis_driver.php
+++ b/system/libraries/Session/drivers/Session_redis_driver.php
@@ -199,7 +199,7 @@
 	 */
 	public function write($session_id, $session_data)
 	{
-		if ( ! isset($this->_redis))
+		if ( ! isset($this->_redis, $this->_lock_key))
 		{
 			return $this->_fail();
 		}
@@ -215,27 +215,22 @@
 			$this->_session_id = $session_id;
 		}
 
-		if (isset($this->_lock_key))
+		$this->_redis->setTimeout($this->_lock_key, 300);
+		if ($this->_fingerprint !== ($fingerprint = md5($session_data)) OR $this->_key_exists === FALSE)
 		{
-			$this->_redis->setTimeout($this->_lock_key, 300);
-			if ($this->_fingerprint !== ($fingerprint = md5($session_data)) OR $this->_key_exists === FALSE)
+			if ($this->_redis->set($this->_key_prefix.$session_id, $session_data, $this->_config['expiration']))
 			{
-				if ($this->_redis->set($this->_key_prefix.$session_id, $session_data, $this->_config['expiration']))
-				{
-					$this->_fingerprint = $fingerprint;
-					$this->_key_exists = TRUE;
-					return $this->_success;
-				}
-
-				return $this->_fail();
+				$this->_fingerprint = $fingerprint;
+				$this->_key_exists = TRUE;
+				return $this->_success;
 			}
 
-			return ($this->_redis->setTimeout($this->_key_prefix.$session_id, $this->_config['expiration']))
-				? $this->_success
-				: $this->_fail();
+			return $this->_fail();
 		}
 
-		return $this->_fail();
+		return ($this->_redis->setTimeout($this->_key_prefix.$session_id, $this->_config['expiration']))
+			? $this->_success
+			: $this->_fail();
 	}
 
 	// ------------------------------------------------------------------------
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 1fe2d46..cb95d17 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -22,6 +22,7 @@
 -  Fixed a bug (#4905) - :doc:`Loader Library <libraries/loader>` didn't take into account possible user-provided directory paths when loading helpers.
 -  Fixed a bug (#4916) - :doc:`Session Library <libraries/sessions>` with ``sess_match_ip`` enabled was unusable for IPv6 clients when using the 'database' driver on MySQL 5.7.5+.
 -  Fixed a bug (#4917) - :doc:`Date Helper <helpers/date_helper>` function :php:func:`nice_date()` didn't handle YYYYMMDD inputs properly.
+-  Fixed a bug (#4923) - :doc:`Session Library <libraries/sessions>` could execute an erroneous SQL query with the 'database' driver, if the lock attempt times out.
 
 Version 3.1.2
 =============