diff --git a/Conf.cpp b/Conf.cpp
index 23f7596..8c07bc6 100644
--- a/Conf.cpp
+++ b/Conf.cpp
@@ -198,6 +198,7 @@ m_fmCTCSSLevel(2.0F),
 m_fmKerchunkTime(0U),
 m_fmHangTime(7U),
 m_fmUseCOS(true),
+m_fmCOSInvert(false),
 m_fmRFAudioBoost(1U),
 m_fmMaxDevLevel(90.0F),
 m_fmExtAudioBoost(1U),
@@ -755,6 +756,8 @@ bool CConf::read()
 			m_fmHangTime = (unsigned int)::atoi(value);
 		else if (::strcmp(key, "UseCOS") == 0)
 			m_fmUseCOS = ::atoi(value) == 1;
+		else if (::strcmp(key, "COSInvert") == 0)
+			m_fmCOSInvert = ::atoi(value) == 1;
 		else if (::strcmp(key, "RFAudioBoost") == 0)
 			m_fmRFAudioBoost = (unsigned int)::atoi(value);
 		else if (::strcmp(key, "MaxDevLevel") == 0)
@@ -1628,6 +1631,11 @@ bool CConf::getFMUseCOS() const
 	return m_fmUseCOS;
 }
 
+bool CConf::getFMCOSInvert() const
+{
+	return m_fmCOSInvert;
+}
+
 unsigned int CConf::getFMRFAudioBoost() const
 {
 	return m_fmRFAudioBoost;
diff --git a/Conf.h b/Conf.h
index 0ba0955..f5a40bd 100644
--- a/Conf.h
+++ b/Conf.h
@@ -196,6 +196,7 @@ public:
   unsigned int getFMKerchunkTime() const;
   unsigned int getFMHangTime() const;
   bool         getFMUseCOS() const;
+  bool         getFMCOSInvert() const;
   unsigned int getFMRFAudioBoost() const;
   float        getFMMaxDevLevel() const;
   unsigned int getFMExtAudioBoost() const;
@@ -462,6 +463,7 @@ private:
   unsigned int m_fmKerchunkTime;
   unsigned int m_fmHangTime;
   bool         m_fmUseCOS;
+  bool         m_fmCOSInvert;
   unsigned int m_fmRFAudioBoost;
   float        m_fmMaxDevLevel;
   unsigned int m_fmExtAudioBoost;
diff --git a/MMDVM.ini b/MMDVM.ini
index 9faaecc..5e71a84 100644
--- a/MMDVM.ini
+++ b/MMDVM.ini
@@ -166,6 +166,7 @@ CTCSSLevel=20
 KerchunkTime=0
 HangTime=7
 UseCOS=1
+COSInvert=0
 RFAudioBoost=1
 MaxDevLevel=90
 ExtAudioBoost=1
diff --git a/MMDVMHost.cpp b/MMDVMHost.cpp
index b3314be..e2a7766 100644
--- a/MMDVMHost.cpp
+++ b/MMDVMHost.cpp
@@ -1231,6 +1231,7 @@ bool CMMDVMHost::createModem()
 		unsigned int kerchunkTime      = m_conf.getFMKerchunkTime();
 		unsigned int hangTime          = m_conf.getFMHangTime();
 		bool         useCOS            = m_conf.getFMUseCOS();
+		bool         cosInvert         = m_conf.getFMCOSInvert();
 		unsigned int rfAudioBoost      = m_conf.getFMRFAudioBoost();
 		float        maxDevLevel       = m_conf.getFMMaxDevLevel();
 		unsigned int extAudioBoost     = m_conf.getFMExtAudioBoost();
@@ -1261,13 +1262,14 @@ bool CMMDVMHost::createModem()
 		LogInfo("    Kerchunk Time: %us", kerchunkTime);
 		LogInfo("    Hang Time: %us", hangTime);
 		LogInfo("    Use COS: %s", useCOS ? "yes" : "no");
+		LogInfo("    COS Invert: %s", cosInvert ? "yes" : "no");
 		LogInfo("    RF Audio Boost: x%u", rfAudioBoost);
 		LogInfo("    Max. Deviation Level: %.1f%%", maxDevLevel);
 		// LogInfo("    Ext. Audio Boost: x%u", extAudioBoost);
 
 		m_modem->setFMCallsignParams(callsign, callsignSpeed, callsignFrequency, callsignTime, callsignHoldoff, callsignHighLevel, callsignLowLevel, callsignAtStart, callsignAtEnd, callsignAtLatch);
 		m_modem->setFMAckParams(rfAck, ackSpeed, ackFrequency, ackMinTime, ackDelay, ackLevel);
-		m_modem->setFMMiscParams(timeout, timeoutLevel, ctcssFrequency, ctcssThreshold, ctcssLevel, kerchunkTime, hangTime, useCOS, rfAudioBoost, maxDevLevel);
+		m_modem->setFMMiscParams(timeout, timeoutLevel, ctcssFrequency, ctcssThreshold, ctcssLevel, kerchunkTime, hangTime, useCOS, cosInvert, rfAudioBoost, maxDevLevel);
 	}
 
 	bool ret = m_modem->open();
diff --git a/Modem.cpp b/Modem.cpp
index 3041567..edbebec 100644
--- a/Modem.cpp
+++ b/Modem.cpp
@@ -193,6 +193,7 @@ m_fmCtcssLevel(10.0F),
 m_fmKerchunkTime(0U),
 m_fmHangTime(5U),
 m_fmUseCOS(true),
+m_fmCOSInvert(false),
 m_fmRFAudioBoost(1U),
 m_fmMaxDevLevel(90.0F)
 {
@@ -1912,7 +1913,7 @@ void CModem::setFMAckParams(const std::string& rfAck, unsigned int ackSpeed, uns
 	m_fmAckLevel     = ackLevel;
 }
 
-void CModem::setFMMiscParams(unsigned int timeout, float timeoutLevel, float ctcssFrequency, unsigned int ctcssThreshold, float ctcssLevel, unsigned int kerchunkTime, unsigned int hangTime, bool useCOS, unsigned int rfAudioBoost, float maxDevLevel)
+void CModem::setFMMiscParams(unsigned int timeout, float timeoutLevel, float ctcssFrequency, unsigned int ctcssThreshold, float ctcssLevel, unsigned int kerchunkTime, unsigned int hangTime, bool useCOS, bool cosInvert, unsigned int rfAudioBoost, float maxDevLevel)
 {
 	m_fmTimeout      = timeout;
 	m_fmTimeoutLevel = timeoutLevel;
@@ -1925,6 +1926,8 @@ void CModem::setFMMiscParams(unsigned int timeout, float timeoutLevel, float ctc
 	m_fmHangTime     = hangTime;
 
 	m_fmUseCOS       = useCOS;
+	m_fmCOSInvert    = cosInvert;
+
 	m_fmRFAudioBoost = rfAudioBoost;
 	m_fmMaxDevLevel  = maxDevLevel;
 }
@@ -2065,6 +2068,8 @@ bool CModem::setFMMiscParams()
 	buffer[10U] = 0x00U;
 	if (m_fmUseCOS)
 		buffer[10U] |= 0x01U;
+	if (m_fmCOSInvert)
+		buffer[10U] |= 0x02U;
 
 	buffer[11U] = m_fmRFAudioBoost;
 
diff --git a/Modem.h b/Modem.h
index edb30ec..6404d89 100644
--- a/Modem.h
+++ b/Modem.h
@@ -47,7 +47,7 @@ public:
 
 	virtual void setFMCallsignParams(const std::string& callsign, unsigned int callsignSpeed, unsigned int callsignFrequency, unsigned int callsignTime, unsigned int callsignHoldoff, float callsignHighLevel, float callsignLowLevel, bool callsignAtStart, bool callsignAtEnd, bool callsignAtLatch);
 	virtual void setFMAckParams(const std::string& rfAck, unsigned int ackSpeed, unsigned int ackFrequency, unsigned int ackMinTime, unsigned int ackDelay, float ackLevel);
-	virtual void setFMMiscParams(unsigned int timeout, float timeoutLevel, float ctcssFrequency, unsigned int ctcssThreshold, float ctcssLevel, unsigned int kerchunkTime, unsigned int hangTime, bool useCOS, unsigned int rfAudioBoost, float maxDevLevel);
+	virtual void setFMMiscParams(unsigned int timeout, float timeoutLevel, float ctcssFrequency, unsigned int ctcssThreshold, float ctcssLevel, unsigned int kerchunkTime, unsigned int hangTime, bool useCOS, bool cosInvert, unsigned int rfAudioBoost, float maxDevLevel);
 
 	virtual bool open();
 
@@ -209,6 +209,7 @@ private:
 	unsigned int               m_fmKerchunkTime;
 	unsigned int               m_fmHangTime;
 	bool                       m_fmUseCOS;
+	bool                       m_fmCOSInvert;
 	unsigned int               m_fmRFAudioBoost;
 	float                      m_fmMaxDevLevel;
 
diff --git a/Version.h b/Version.h
index 4b0d9cc..7bf2d5a 100644
--- a/Version.h
+++ b/Version.h
@@ -19,6 +19,6 @@
 #if !defined(VERSION_H)
 #define	VERSION_H
 
-const char* VERSION = "20200504";
+const char* VERSION = "20200506";
 
 #endif