diff --git a/src/Module.cpp b/src/Module.cpp
index 438eda19..1c994eff 100644
--- a/src/Module.cpp
+++ b/src/Module.cpp
@@ -7,7 +7,7 @@ Module::Module(int rx, int tx, HardwareSerial* useSer) {
   _int0 = -1;
   _int1 = -1;
 
-#if SOFTWARE_SERIAL_UNSUPPORTED
+#ifdef SOFTWARE_SERIAL_UNSUPPORTED
   ModuleSerial = useSer;
 #else
   ModuleSerial = new SoftwareSerial(_rx, _tx);
@@ -34,7 +34,7 @@ Module::Module(int cs, int int0, int int1, int rx, int tx, SPIClass& spi, SPISet
   _spi = &spi;
   _spiSettings = spiSettings;
 
-#if SOFTWARE_SERIAL_UNSUPPORTED
+#ifdef SOFTWARE_SERIAL_UNSUPPORTED
   ModuleSerial = useSer;
 #else
   ModuleSerial = new SoftwareSerial(_rx, _tx);
diff --git a/src/Module.h b/src/Module.h
index aae70da8..8bddd4b3 100644
--- a/src/Module.h
+++ b/src/Module.h
@@ -27,7 +27,7 @@ class Module {
 
       \param serial HardwareSerial to be used on ESP32 and SAMD. Defaults to 1
     */
-#if SOFTWARE_SERIAL_UNSUPPORTED
+#ifdef SOFTWARE_SERIAL_UNSUPPORTED
     Module(int tx, int rx, HardwareSerial* useSer = &Serial1);
 #else
     Module(int tx, int rx, HardwareSerial* useSer = nullptr);
@@ -84,7 +84,7 @@ class Module {
 
       \param serial HardwareSerial to be used on ESP32 and SAMD. Defaults to 1
     */
-#if SOFTWARE_SERIAL_UNSUPPORTED
+#ifdef SOFTWARE_SERIAL_UNSUPPORTED
     Module(int cs, int int0, int int1, int rx, int tx, SPIClass& spi = SPI, SPISettings spiSettings = SPISettings(2000000, MSBFIRST, SPI_MODE0), HardwareSerial* useSer = &Serial1);
 #else
     Module(int cs, int int0, int int1, int rx, int tx, SPIClass& spi = SPI, SPISettings spiSettings = SPISettings(2000000, MSBFIRST, SPI_MODE0), HardwareSerial* useSer = nullptr);
@@ -96,7 +96,7 @@ class Module {
     /*!
       \brief Internal SoftwareSerial instance.
     */
-#if SOFTWARE_SERIAL_UNSUPPORTED
+#ifdef SOFTWARE_SERIAL_UNSUPPORTED
     HardwareSerial* ModuleSerial;
 #else
     SoftwareSerial* ModuleSerial;
diff --git a/src/TypeDef.h b/src/TypeDef.h
index 2099187c..41f4ba5c 100644
--- a/src/TypeDef.h
+++ b/src/TypeDef.h
@@ -8,7 +8,9 @@
 #endif
 
 // the following platforms do not support SoftwareSerial library
-#define SOFTWARE_SERIAL_UNSUPPORTED (defined(ESP32) || defined(SAMD_SERIES) || defined (ARDUINO_ARCH_STM32))
+#if defined(ESP32) || defined(SAMD_SERIES) || defined(ARDUINO_ARCH_STM32)
+  #define SOFTWARE_SERIAL_UNSUPPORTED
+#endif
 
 // uncomment to enable static-only memory management: no dynamic allocation will be performed
 // Warning: Large static arrays will be created in some methods. It is also not advised to send large packets in this mode.