diff --git a/master/master.c b/master/master.c
index ca3ee727..37a3e7c3 100644
--- a/master/master.c
+++ b/master/master.c
@@ -109,7 +109,7 @@ int ec_master_init(ec_master_t *master, /**< EtherCAT master */
 
     master->index = index;
     master->device = NULL;
-    master->reserved = 0;
+    atomic_set(&master->available, 1);
     INIT_LIST_HEAD(&master->slaves);
     INIT_LIST_HEAD(&master->datagram_queue);
     INIT_LIST_HEAD(&master->domains);
diff --git a/master/master.h b/master/master.h
index e489d829..31caa5b8 100644
--- a/master/master.h
+++ b/master/master.h
@@ -44,6 +44,7 @@
 #include <linux/list.h>
 #include <linux/sysfs.h>
 #include <linux/timer.h>
+#include <asm/atomic.h>
 
 #include "device.h"
 #include "domain.h"
@@ -92,7 +93,7 @@ ec_stats_t;
 struct ec_master
 {
     struct list_head list; /**< list item for module's master list */
-    unsigned int reserved; /**< non-zero, if the master is reserved for RT */
+    atomic_t available; /**< zero, if the master is reserved for RT */
     unsigned int index; /**< master index */
 
     struct kobject kobj; /**< kobject */
diff --git a/master/module.c b/master/module.c
index fd0dda74..47996cf3 100644
--- a/master/module.c
+++ b/master/module.c
@@ -409,11 +409,11 @@ ec_master_t *ecrt_request_master(unsigned int master_index
 
     if (!(master = ec_find_master(master_index))) goto out_return;
 
-    if (master->reserved) {
+    if (!atomic_dec_and_test(&master->available)) {
+        atomic_inc(&master->available);
         EC_ERR("Master %i is already in use!\n", master_index);
         goto out_return;
     }
-    master->reserved = 1;
 
     if (!master->device) {
         EC_ERR("Master %i has no assigned device!\n", master_index);
@@ -452,7 +452,7 @@ ec_master_t *ecrt_request_master(unsigned int master_index
  out_module_put:
     module_put(master->device->module);
  out_release:
-    master->reserved = 0;
+    atomic_inc(&master->available);
  out_return:
     EC_ERR("Failed to request master %i.\n", master_index);
     return NULL;
@@ -469,7 +469,7 @@ void ecrt_release_master(ec_master_t *master /**< EtherCAT master */)
 {
     EC_INFO("Releasing master %i...\n", master->index);
 
-    if (!master->reserved) {
+    if (atomic_read(&master->available)) {
         EC_ERR("Master %i was never requested!\n", master->index);
         return;
     }
@@ -478,7 +478,7 @@ void ecrt_release_master(ec_master_t *master /**< EtherCAT master */)
     ec_master_idle_start(master);
 
     module_put(master->device->module);
-    master->reserved = 0;
+    atomic_inc(&master->available);
 
     EC_INFO("Successfully released master %i.\n", master->index);
     return;