diff --git a/HD44780.cpp b/HD44780.cpp
index e581b94..79e2e19 100644
--- a/HD44780.cpp
+++ b/HD44780.cpp
@@ -44,7 +44,6 @@ m_dmr(false)
 {
 	assert(rows > 1U);
 	assert(cols > 15U);
-	assert(callsign.c_str() != NULL);
 }
 
 CHD44780::~CHD44780()
@@ -212,8 +211,6 @@ void CHD44780::clearDStar()
 
 void CHD44780::writeDMR(unsigned int slotNo, const std::string& src, bool group, const std::string& dst, const char* type)
 {
-	assert(src.c_str() != NULL);
-	assert(dst.c_str() != NULL);
 	assert(type != NULL);
 
 	if (!m_dmr) {
diff --git a/Nextion.cpp b/Nextion.cpp
index d0d24f1..290606b 100644
--- a/Nextion.cpp
+++ b/Nextion.cpp
@@ -30,7 +30,6 @@ m_serial(port, SERIAL_9600),
 m_brightness(brightness),
 m_mode(MODE_IDLE)
 {
-	assert(callsign.c_str() != NULL);
 	assert(brightness >= 0U && brightness <= 100U);
 }
 
@@ -127,8 +126,6 @@ void CNextion::clearDStar()
 
 void CNextion::writeDMR(unsigned int slotNo, const std::string& src, bool group, const std::string& dst, const char* type)
 {
-	assert(src.c_str() != NULL);
-	assert(dst.c_str() != NULL);
 	assert(type != NULL);
 
 	if (m_mode != MODE_DMR) {
diff --git a/TFTSerial.cpp b/TFTSerial.cpp
index 8975fdf..8b413c1 100644
--- a/TFTSerial.cpp
+++ b/TFTSerial.cpp
@@ -51,7 +51,6 @@ m_serial(port, SERIAL_9600),
 m_brightness(brightness),
 m_mode(MODE_IDLE)
 {
-	assert(callsign.c_str() != NULL);
 	assert(brightness >= 0U && brightness <= 100U);
 }
 
@@ -190,8 +189,6 @@ void CTFTSerial::clearDStar()
 
 void CTFTSerial::writeDMR(unsigned int slotNo, const std::string& src, bool group, const std::string& dst, const char* type)
 {
-	assert(src.c_str() != NULL);
-	assert(dst.c_str() != NULL);
 	assert(type != NULL);
 
 	if (m_mode != MODE_DMR) {