diff --git a/include/Callbackable.h b/include/Callbackable.h
index 58501c455b..c22d95a40a 100644
--- a/include/Callbackable.h
+++ b/include/Callbackable.h
@@ -17,6 +17,8 @@
 #ifndef CALLBACKABLE_H_
 #define CALLBACKABLE_H_
 
+#include <pthread.h>
+
 using namespace std;
 
 /**
@@ -27,9 +29,15 @@ class Callbackable
 {
 public:
 
-    Callbackable():cb(0),arg(0){};
+    Callbackable():cb(0),arg(0)
+    {
+        pthread_mutex_init(&mutex,0);
+    };
 
-    virtual ~Callbackable(){};
+    virtual ~Callbackable()
+    {
+        pthread_mutex_destroy(&mutex);
+    };
 
     /**
      *  Datatype for call back pointers
@@ -38,12 +46,14 @@ public:
 
     /**
      *  Set the callback function and custom arguments to be executed by the
-     *  next SQL command
+     *  next SQL command, and locks the mutex until unset_callback is called.
      *    @param ptr to the callback function
      *    @param arg custom arguments for the callback function
      */
     void set_callback(Callback _cb, void * _arg = 0)
     {
+        pthread_mutex_lock(&mutex);
+
         cb  = _cb;
         arg = _arg;
     };
@@ -58,16 +68,26 @@ public:
     };
 
     /**
-     *  Set the callback function and custom arguments to be executed by the
-     *  next SQL command
-     *    @param ptr to the callback function
-     *    @param arg custom arguments for the callback function
+     *  Call the callback funcion set. This method must be called only if
+     *  isCallBackSet returns true.
+     *      @return the callback function return value.
      */
     int do_callback(int num, char **values, char **names)
     {
         return (this->*cb)(arg, num, values, names);
     };
 
+    /**
+     *  Unset the callback function.
+     */
+    void unset_callback()
+    {
+        cb  = 0;
+        arg = 0;
+
+        pthread_mutex_unlock(&mutex);
+    }
+
 private:
     /**
      *  SQL callback to be executed for each row result of an SQL statement
@@ -78,6 +98,11 @@ private:
      *  Custom arguments for the callback
      */
     void *   arg;
+
+    /**
+     *  Mutex for locking the callback function.
+     */
+    pthread_mutex_t             mutex;
 };
 
 #endif /*CALLBACKABLE_H_*/
diff --git a/src/host/Host.cc b/src/host/Host.cc
index 9309869286..bd3db54333 100644
--- a/src/host/Host.cc
+++ b/src/host/Host.cc
@@ -110,6 +110,8 @@ int Host::select(SqlDB *db)
 
     rc = db->exec(oss, this);
 
+    unset_callback();
+
     if ((rc != 0) || (oid != boid ))
     {
         return -1;
diff --git a/src/host/HostPool.cc b/src/host/HostPool.cc
index 10497204ec..ad1997c085 100644
--- a/src/host/HostPool.cc
+++ b/src/host/HostPool.cc
@@ -84,6 +84,8 @@ int HostPool::discover(map<int, string> * discovered_hosts)
 
     rc = db->exec(sql,this);
 
+    unset_callback();
+
     return rc;
 }
 
@@ -123,5 +125,7 @@ int HostPool::dump(ostringstream& oss, const string& where)
 
     oss << "</HOST_POOL>";
 
+    unset_callback();
+
     return rc;
 }
diff --git a/src/host/HostShare.cc b/src/host/HostShare.cc
index eb1cbf9e51..b9b92a0247 100644
--- a/src/host/HostShare.cc
+++ b/src/host/HostShare.cc
@@ -184,6 +184,8 @@ int HostShare::select(SqlDB * db)
 
     rc = db->exec(oss,this);
 
+    unset_callback();
+
     if (hsid != bhsid )
     {
         rc = -1;
diff --git a/src/pool/PoolSQL.cc b/src/pool/PoolSQL.cc
index 6615d0c23d..f904a293cd 100644
--- a/src/pool/PoolSQL.cc
+++ b/src/pool/PoolSQL.cc
@@ -61,6 +61,8 @@ PoolSQL::PoolSQL(SqlDB * _db, const char * table): db(_db), lastOID(-1)
     oss << "SELECT MAX(oid) FROM " << table;
 
     db->exec(oss,this);
+
+    unset_callback();
 };
 
 /* -------------------------------------------------------------------------- */
@@ -302,5 +304,7 @@ int PoolSQL::search(
 
     rc = db->exec(sql, this);
 
+    unset_callback();
+
     return rc;
 }
diff --git a/src/pool/test/TestPoolSQL.cc b/src/pool/test/TestPoolSQL.cc
index 8e6fe4ed3f..dc0f63f410 100644
--- a/src/pool/test/TestPoolSQL.cc
+++ b/src/pool/test/TestPoolSQL.cc
@@ -73,6 +73,8 @@ int TestObjectSQL::select(SqlDB *db)
 
     rc = db->exec(oss, this);
 
+    unset_callback();
+
     if ((rc != 0) || (oid != boid ))
     {
         return -1;
diff --git a/src/template/TemplateSQL.cc b/src/template/TemplateSQL.cc
index 701cc7e0c1..760fee7738 100644
--- a/src/template/TemplateSQL.cc
+++ b/src/template/TemplateSQL.cc
@@ -61,6 +61,8 @@ int TemplateSQL::insert(SqlDB * db)
 
     rc = db->exec(oss,this);
 
+    unset_callback();
+
     if ( rc != 0 )
     {
         return -1;
@@ -231,6 +233,8 @@ int TemplateSQL::select(SqlDB * db)
 
     rc = db->exec(oss,this);
 
+    unset_callback();
+
     return rc;
 }
 
diff --git a/src/um/User.cc b/src/um/User.cc
index fbf9768dbf..abcf2f4ade 100644
--- a/src/um/User.cc
+++ b/src/um/User.cc
@@ -98,6 +98,8 @@ int User::select(SqlDB *db)
 
     rc = db->exec(oss, this);
 
+    unset_callback();
+
     if ((rc != 0) || (oid != boid ))
     {
         return -1;
diff --git a/src/um/UserPool.cc b/src/um/UserPool.cc
index 42b46dc6a6..f7293ada1b 100644
--- a/src/um/UserPool.cc
+++ b/src/um/UserPool.cc
@@ -53,6 +53,8 @@ UserPool::UserPool(SqlDB * db):PoolSQL(db,User::table)
 
     db->exec(sql, this);
 
+    unset_callback();
+
     if ((int) known_users.size() == 0)
     {
         // User oneadmin needs to be added in the bootstrap
@@ -217,7 +219,9 @@ int UserPool::dump(ostringstream& oss, const string& where)
 
     rc = db->exec(cmd, this);
 
+    unset_callback();
+
     oss << "</USER_POOL>";
 
     return rc;
-}
\ No newline at end of file
+}
diff --git a/src/vm/History.cc b/src/vm/History.cc
index d73ab00927..9a74b9d813 100644
--- a/src/vm/History.cc
+++ b/src/vm/History.cc
@@ -371,6 +371,8 @@ int History::select(SqlDB * db)
 
     rc = db->exec(oss,this);
 
+    unset_callback();
+
     if ( rc == 0 ) // Regenerate non-persistent data
     {
         non_persistent_data();
diff --git a/src/vm/VirtualMachine.cc b/src/vm/VirtualMachine.cc
index 97089edb89..c26dfa3b9a 100644
--- a/src/vm/VirtualMachine.cc
+++ b/src/vm/VirtualMachine.cc
@@ -165,6 +165,8 @@ int VirtualMachine::select(SqlDB * db)
 
     rc = db->exec(oss,this);
 
+    unset_callback();
+
     if ((rc != 0) || (oid != boid ))
     {
         goto error_id;
diff --git a/src/vm/VirtualMachinePool.cc b/src/vm/VirtualMachinePool.cc
index 47e785f39b..7e2e20bb60 100644
--- a/src/vm/VirtualMachinePool.cc
+++ b/src/vm/VirtualMachinePool.cc
@@ -455,5 +455,7 @@ int VirtualMachinePool::dump(ostringstream& oss, const string& where)
 
     oss << "</VM_POOL>";
 
+    unset_callback();
+
     return rc;
 }
diff --git a/src/vnm/Leases.cc b/src/vnm/Leases.cc
index d2478b3ecf..8813e7d2aa 100644
--- a/src/vnm/Leases.cc
+++ b/src/vnm/Leases.cc
@@ -314,6 +314,8 @@ int Leases::select(SqlDB * db)
 
     rc = db->exec(oss,this);
 
+    unset_callback();
+
     if (rc != 0)
     {
         goto error_id;
diff --git a/src/vnm/VirtualNetwork.cc b/src/vnm/VirtualNetwork.cc
index 416f685b90..7a051ef5ed 100644
--- a/src/vnm/VirtualNetwork.cc
+++ b/src/vnm/VirtualNetwork.cc
@@ -111,6 +111,8 @@ int VirtualNetwork::select(SqlDB * db)
 
     rc = db->exec(oss, this);
 
+    unset_callback();
+
     if ((rc != 0) || (oid != boid ))
     {
         goto error_id;
diff --git a/src/vnm/VirtualNetworkPool.cc b/src/vnm/VirtualNetworkPool.cc
index a52e3b6b0e..28e1b01789 100644
--- a/src/vnm/VirtualNetworkPool.cc
+++ b/src/vnm/VirtualNetworkPool.cc
@@ -173,6 +173,8 @@ VirtualNetwork * VirtualNetworkPool::get(const string& name, bool lock)
 
     rc = db->exec(oss, this);
 
+    unset_callback();
+
     db->free_str(sql_name);
 
     if (rc != 0 || oid == -1)
@@ -232,5 +234,7 @@ int VirtualNetworkPool::dump(ostringstream& oss, const string& where)
 
     oss << "</VNET_POOL>";
 
+    unset_callback();
+
     return rc;
-}
\ No newline at end of file
+}