diff --git a/V203/usb/ch32v203/usart.cpp b/V203/usb/ch32v203/usart.cpp
index 30c17a8..5f168eb 100644
--- a/V203/usb/ch32v203/usart.cpp
+++ b/V203/usb/ch32v203/usart.cpp
@@ -69,6 +69,7 @@ uint32_t Usart::Down(const char * data, const uint32_t len) {
   return n;
 }
 void Usart::SetBaud (const uint32_t _baud) const {
+  if (_baud == 0u) return;                // ! zero divide
   const ONE_BIT b = USART1.CTLR1.B.UE;
   if (b == SET) USART1.CTLR1.B.UE = RESET;
   const uint32_t HCLK = SystemCoreClock;  // hodiny pro USART zde nejsou děleny