diff --git a/include/MySQL_HostGroups_Manager.h b/include/MySQL_HostGroups_Manager.h
index 44ac6d3b9..9da9d6684 100644
--- a/include/MySQL_HostGroups_Manager.h
+++ b/include/MySQL_HostGroups_Manager.h
@@ -10,6 +10,8 @@
 #define STRESSTEST_POOL
 */
 
+#define MHM_PTHREAD_MUTEX
+
 #define MYHGM_MYSQL_SERVERS "CREATE TABLE mysql_servers ( hostgroup_id INT NOT NULL DEFAULT 0 , hostname VARCHAR NOT NULL , port INT NOT NULL DEFAULT 3306 , weight INT CHECK (weight >= 0) NOT NULL DEFAULT 1 , status INT CHECK (status IN (0, 1, 2, 3, 4)) NOT NULL DEFAULT 0 , compression INT CHECK (compression >=0 AND compression <= 102400) NOT NULL DEFAULT 0 , max_connections INT CHECK (max_connections >=0) NOT NULL DEFAULT 1000 , max_replication_lag INT CHECK (max_replication_lag >= 0 AND max_replication_lag <= 126144000) NOT NULL DEFAULT 0 , use_ssl INT CHECK (use_ssl IN(0,1)) NOT NULL DEFAULT 0 , max_latency_ms INT UNSIGNED CHECK (max_latency_ms>=0) NOT NULL DEFAULT 0 , comment VARCHAR NOT NULL DEFAULT '' , mem_pointer INT NOT NULL DEFAULT 0 , PRIMARY KEY (hostgroup_id, hostname, port) )"
 #define MYHGM_MYSQL_SERVERS_INCOMING "CREATE TABLE mysql_servers_incoming ( hostgroup_id INT NOT NULL DEFAULT 0 , hostname VARCHAR NOT NULL , port INT NOT NULL DEFAULT 3306 , weight INT CHECK (weight >= 0) NOT NULL DEFAULT 1 , status INT CHECK (status IN (0, 1, 2, 3, 4)) NOT NULL DEFAULT 0 , compression INT CHECK (compression >=0 AND compression <= 102400) NOT NULL DEFAULT 0 , max_connections INT CHECK (max_connections >=0) NOT NULL DEFAULT 1000 , max_replication_lag INT CHECK (max_replication_lag >= 0 AND max_replication_lag <= 126144000) NOT NULL DEFAULT 0 , use_ssl INT CHECK (use_ssl IN(0,1)) NOT NULL DEFAULT 0 , max_latency_ms INT UNSIGNED CHECK (max_latency_ms>=0) NOT NULL DEFAULT 0 , comment VARCHAR NOT NULL DEFAULT '' , PRIMARY KEY (hostgroup_id, hostname, port))"
 #define MYHGM_MYSQL_REPLICATION_HOSTGROUPS "CREATE TABLE mysql_replication_hostgroups (writer_hostgroup INT CHECK (writer_hostgroup>=0) NOT NULL PRIMARY KEY , reader_hostgroup INT NOT NULL CHECK (reader_hostgroup<>writer_hostgroup AND reader_hostgroup>0) , comment VARCHAR , UNIQUE (reader_hostgroup))"
@@ -121,7 +123,11 @@ class MySQL_HostGroups_Manager {
 	private:
 	SQLite3DB	*admindb;
 	SQLite3DB	*mydb;
+#ifdef MHM_PTHREAD_MUTEX
+	pthread_mutex_t lock;
+#else
 	rwlock_t rwlock;
+#endif
 	PtrArray *MyHostGroups;
 
 	MyHGC * MyHGC_find(unsigned int);
@@ -156,8 +162,8 @@ class MySQL_HostGroups_Manager {
 	} status;
 	MySQL_HostGroups_Manager();
 	~MySQL_HostGroups_Manager();
-	void rdlock();
-	void rdunlock();
+//	void rdlock();
+//	void rdunlock();
 	void wrlock();
 	void wrunlock();
 	bool server_add(unsigned int hid, char *add, uint16_t p=3306, unsigned int _weight=1, enum MySerStatus status=MYSQL_SERVER_STATUS_ONLINE, unsigned int _comp=0, unsigned int _max_connections=100, unsigned int _max_replication_lag=0, unsigned int _use_ssl=0, unsigned int _max_latency_ms=0, char *comment=NULL);
diff --git a/lib/MySQL_HostGroups_Manager.cpp b/lib/MySQL_HostGroups_Manager.cpp
index 2fa4baa91..980f5ca18 100644
--- a/lib/MySQL_HostGroups_Manager.cpp
+++ b/lib/MySQL_HostGroups_Manager.cpp
@@ -279,7 +279,11 @@ MySQL_HostGroups_Manager::MySQL_HostGroups_Manager() {
 	status.autocommit_cnt_filtered=0;
 	status.commit_cnt_filtered=0;
 	status.rollback_cnt_filtered=0;
+#ifdef MHM_PTHREAD_MUTEX
+	pthread_mutex_init(&lock, NULL);
+#else
 	spinlock_rwlock_init(&rwlock);
+#endif
 	admindb=NULL;	// initialized only if needed
 	mydb=new SQLite3DB();
 	mydb->open((char *)"file:mem_mydb?mode=memory&cache=shared", SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE | SQLITE_OPEN_FULLMUTEX);
@@ -300,8 +304,12 @@ MySQL_HostGroups_Manager::~MySQL_HostGroups_Manager() {
 	if (admindb) {
 		delete admindb;
 	}
+#ifdef MHM_PTHREAD_MUTEX
+	pthread_mutex_destroy(&lock);
+#endif
 }
 
+/*
 void MySQL_HostGroups_Manager::rdlock() {
 	spin_wrlock(&rwlock);
 }
@@ -309,15 +317,23 @@ void MySQL_HostGroups_Manager::rdlock() {
 void MySQL_HostGroups_Manager::rdunlock() {
 	spin_wrunlock(&rwlock);
 }
-
+*/
 
 // wrlock() is only required during commit()
 void MySQL_HostGroups_Manager::wrlock() {
+#ifdef MHM_PTHREAD_MUTEX
+	pthread_mutex_lock(&lock);
+#else
 	spin_wrlock(&rwlock);
+#endif
 }
 
 void MySQL_HostGroups_Manager::wrunlock() {
+#ifdef MHM_PTHREAD_MUTEX
+	pthread_mutex_unlock(&lock);
+#else
 	spin_wrunlock(&rwlock);
+#endif
 }
 
 unsigned int MySQL_HostGroups_Manager::get_servers_table_version() {