diff --git a/src/SoftwareSerial.cpp b/src/SoftwareSerial.cpp
index f058954..3b824a8 100644
--- a/src/SoftwareSerial.cpp
+++ b/src/SoftwareSerial.cpp
@@ -52,10 +52,12 @@ __attribute__((always_inline)) inline void IRAM_ATTR UARTBase::restoreInterrupts
 constexpr uint8_t BYTE_ALL_BITS_SET = ~static_cast<uint8_t>(0);
 
 UARTBase::UARTBase() {
+    m_isrOverflow = false;
 }
 
 UARTBase::UARTBase(int8_t rxPin, int8_t txPin, bool invert)
 {
+    m_isrOverflow = false;
     m_rxPin = rxPin;
     m_txPin = txPin;
     m_invert = invert;
diff --git a/src/SoftwareSerial.h b/src/SoftwareSerial.h
index d6f1a57..bd92f8a 100644
--- a/src/SoftwareSerial.h
+++ b/src/SoftwareSerial.h
@@ -292,7 +292,7 @@ class UARTBase : public Stream {
     // Member variables
     int8_t m_rxPin = -1;
     int8_t m_txPin = -1;
-    bool m_invert;
+    bool m_invert = false;
 
 private:
     // It's legal to exceed the deadline, for instance,
@@ -367,7 +367,7 @@ class UARTBase : public Stream {
     // 1 = positive including 0, 0 = negative.
     std::unique_ptr<circular_queue<uint32_t, UARTBase*> > m_isrBuffer;
     const Delegate<void(uint32_t&&), UARTBase*> m_isrBufferForEachDel = { [](UARTBase* self, uint32_t&& isrTick) { self->rxBits(isrTick); }, this };
-    std::atomic<bool> m_isrOverflow = false;
+    std::atomic<bool> m_isrOverflow;
     uint32_t m_isrLastTick;
     bool m_rxCurParity = false;
     Delegate<void(), void*> m_rxHandler;