diff --git a/client/flasher.c b/client/flasher.c
index 6019a6b93..3ed438452 100644
--- a/client/flasher.c
+++ b/client/flasher.c
@@ -72,7 +72,7 @@ void CloseProxmark() {
 
 int OpenProxmark(size_t i) {
   sp = uart_open(serial_port_name);
-  if (sp == INVALID_SERIAL_PORT) {
+  if (sp == INVALID_SERIAL_PORT || sp == CLAIMED_SERIAL_PORT) {
     //poll once a second
     return 0;
   }
diff --git a/client/proxmark3.c b/client/proxmark3.c
index 81f2c18a0..78bc1fe47 100644
--- a/client/proxmark3.c
+++ b/client/proxmark3.c
@@ -221,11 +221,16 @@ int main(int argc, char* argv[]) {
     offline = 0;
   }
 */
+  
   sp = uart_open(argv[1]);
   if (sp == INVALID_SERIAL_PORT) {
     printf("ERROR: invalid serial port\n");
     marg.usb_present = 0;
     offline = 1;
+  } else if (sp == CLAIMED_SERIAL_PORT) {
+    printf("ERROR: serial port is claimed by another process\n");
+    marg.usb_present = 0;
+    offline = 1;
   } else {
     marg.usb_present = 1;
     offline = 0;