diff --git a/master/ioctl.c b/master/ioctl.c
index 100db4bb..43a98c1a 100644
--- a/master/ioctl.c
+++ b/master/ioctl.c
@@ -1899,7 +1899,9 @@ static ATTRIBUTES int ec_ioctl_send(
         return -EPERM;
     }
 
+    down( & master->io_sem );
     ecrt_master_send(master);
+    up( & master->io_sem );
     return 0;
 }
 
@@ -1919,7 +1921,9 @@ static ATTRIBUTES int ec_ioctl_receive(
         return -EPERM;
     }
 
+    down( & master->io_sem );
     ecrt_master_receive(master);
+    up( & master->io_sem );
     return 0;
 }
 
@@ -2018,7 +2022,9 @@ static ATTRIBUTES int ec_ioctl_sync_ref(
         return -EPERM;
     }
 
+    down( & master->io_sem );
     ecrt_master_sync_reference_clock(master);
+    up( & master->io_sem );
     return 0;
 }
 
@@ -2043,7 +2049,9 @@ static ATTRIBUTES int ec_ioctl_sync_ref_to(
         return -EFAULT;
     }
 
+    down( & master->io_sem );
     ecrt_master_sync_reference_clock_to(master, time);
+    up( & master->io_sem );
     return 0;
 }
 
@@ -2063,7 +2071,9 @@ static ATTRIBUTES int ec_ioctl_sync_slaves(
         return -EPERM;
     }
 
+    down( & master->io_sem );
     ecrt_master_sync_slave_clocks(master);
+    up( & master->io_sem );
     return 0;
 }
 
@@ -2114,7 +2124,9 @@ static ATTRIBUTES int ec_ioctl_sync_mon_queue(
         return -EPERM;
     }
 
+    down( & master->io_sem );
     ecrt_master_sync_monitor_queue(master);
+    up( & master->io_sem );
     return 0;
 }
 
@@ -3177,7 +3189,9 @@ static ATTRIBUTES int ec_ioctl_domain_queue(
         return -ENOENT;
     }
 
+    down( & master->io_sem );
     ecrt_domain_queue(domain);
+    up( & master->io_sem );
     return 0;
 }
 
@@ -3895,7 +3909,9 @@ static ATTRIBUTES int ec_ioctl_voe_exec(
         return -ENOENT;
     }
 
+    down( & master->io_sem );
     data.state = ecrt_voe_handler_execute(voe);
+    up( & master->io_sem );
     if (data.state == EC_REQUEST_SUCCESS && voe->dir == EC_DIR_INPUT)
         data.size = ecrt_voe_handler_data_size(voe);
     else