diff --git a/features/unsupported/USBDevice/USBAudio/USBAudio.cpp b/features/unsupported/USBDevice/USBAudio/USBAudio.cpp
index aab9e774e3..a0527aaa5d 100644
--- a/features/unsupported/USBDevice/USBAudio/USBAudio.cpp
+++ b/features/unsupported/USBDevice/USBAudio/USBAudio.cpp
@@ -313,7 +313,8 @@ void USBAudio::USBCallback_requestCompleted(uint8_t * buf, uint32_t length) {
                 switch (transfer->setup.bRequest) {
                     case REQUEST_SET_CUR:
                         mute = data & 0xff;
-                        updateVol.call();
+                        if (updateVol)
+                            updateVol.call();
                         break;
                     default:
                         break;
@@ -324,7 +325,8 @@ void USBAudio::USBCallback_requestCompleted(uint8_t * buf, uint32_t length) {
                     case REQUEST_SET_CUR:
                         volCur = data;
                         volume = (float)volCur/(float)volMax;
-                        updateVol.call();
+                        if (updateVol)
+                            updateVol.call();
                         break;
                     default:
                         break;
diff --git a/features/unsupported/USBDevice/USBSerial/USBSerial.cpp b/features/unsupported/USBDevice/USBSerial/USBSerial.cpp
index 4dc28b9e3c..03e039e63f 100644
--- a/features/unsupported/USBDevice/USBSerial/USBSerial.cpp
+++ b/features/unsupported/USBDevice/USBSerial/USBSerial.cpp
@@ -56,8 +56,9 @@ bool USBSerial::EPBULK_OUT_callback() {
         buf.queue(c[i]);
     }
 
-    //call a potential handler
-    rx.call();
+    //call a potential handlenr
+    if (rx)
+        rx.call();
 
     return true;
 }