diff --git a/src/emucore/AtariVox.cxx b/src/emucore/AtariVox.cxx
index 994b494cf..fd75024e4 100644
--- a/src/emucore/AtariVox.cxx
+++ b/src/emucore/AtariVox.cxx
@@ -50,10 +50,11 @@ bool AtariVox::read(DigitalPin pin)
   switch(pin)
   {
     // Pin 2: SpeakJet READY
-    //        CTS enabled means the SpeakJet can accept more data
+    //        CTS (Clear To Send) is connected inverted
+    //        So CTS = 0 means the buffer is full, which pulls pin 2 high
     case DigitalPin::Two:
     {
-      return setPin(pin, mySerialPort->isCTS());
+      return setPin(pin, !mySerialPort->isCTS());
     }
 
     default:
diff --git a/src/macos/SerialPortMACOS.cxx b/src/macos/SerialPortMACOS.cxx
index 90235e0a8..9745eceff 100644
--- a/src/macos/SerialPortMACOS.cxx
+++ b/src/macos/SerialPortMACOS.cxx
@@ -73,3 +73,15 @@ bool SerialPortMACOS::writeByte(uInt8 data)
   }
   return false;
 }
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+bool SerialPortMACOS::isCTS()
+{
+  if(myHandle)
+  {
+    int status = 0;
+    ioctl(myHandle, TIOCMGET, &status);
+    return status & TIOCM_CTS;
+  }
+  return false;
+}
diff --git a/src/macos/SerialPortMACOS.hxx b/src/macos/SerialPortMACOS.hxx
index 0c83e5045..3d71d5135 100644
--- a/src/macos/SerialPortMACOS.hxx
+++ b/src/macos/SerialPortMACOS.hxx
@@ -48,6 +48,13 @@ class SerialPortMACOS : public SerialPort
     */
     bool writeByte(uInt8 data) override;
 
+  /**
+    Test for 'Clear To Send' enabled.
+
+    @return  True if CTS signal enabled, else false
+  */
+  bool isCTS() override;
+
   private:
     // File descriptor for serial connection
     int myHandle{0};
diff --git a/src/unix/SerialPortUNIX.cxx b/src/unix/SerialPortUNIX.cxx
index f114e18fe..1105d2092 100644
--- a/src/unix/SerialPortUNIX.cxx
+++ b/src/unix/SerialPortUNIX.cxx
@@ -49,6 +49,9 @@ bool SerialPortUNIX::openPort(const string& device)
   if(myHandle <= 0)
     return false;
 
+  // Open the device in nonblocking mode
+  fcntl(myHandle, F_SETFL, FNDELAY);
+
   struct termios termios;
   memset(&termios, 0, sizeof(struct termios));
 
@@ -71,3 +74,15 @@ bool SerialPortUNIX::writeByte(uInt8 data)
   }
   return false;
 }
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+bool SerialPortUNIX::isCTS()
+{
+  if(myHandle)
+  {
+    int status = 0;
+    ioctl(myHandle, TIOCMGET, &status);
+    return status & TIOCM_CTS;
+  }
+  return false;
+}
diff --git a/src/unix/SerialPortUNIX.hxx b/src/unix/SerialPortUNIX.hxx
index b46d0a64a..7a675298e 100644
--- a/src/unix/SerialPortUNIX.hxx
+++ b/src/unix/SerialPortUNIX.hxx
@@ -48,6 +48,13 @@ class SerialPortUNIX : public SerialPort
     */
     bool writeByte(uInt8 data) override;
 
+    /**
+      Test for 'Clear To Send' enabled.
+
+      @return  True if CTS signal enabled, else false
+    */
+    bool isCTS() override;
+
   private:
     // File descriptor for serial connection
     int myHandle{0};
diff --git a/src/windows/SerialPortWINDOWS.cxx b/src/windows/SerialPortWINDOWS.cxx
index 51ed73247..91b6c0bb3 100644
--- a/src/windows/SerialPortWINDOWS.cxx
+++ b/src/windows/SerialPortWINDOWS.cxx
@@ -79,3 +79,15 @@ bool SerialPortWINDOWS::writeByte(uInt8 data)
   }
   return false;
 }
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+bool SerialPortWINDOWS::isCTS()
+{
+  if(myHandle)
+  {
+    DWORD modemStat;
+    GetCommModemStatus(myHandle, &modemStat);
+    return modemStat & MS_CTS_ON;
+  }
+  return false;
+}
diff --git a/src/windows/SerialPortWINDOWS.hxx b/src/windows/SerialPortWINDOWS.hxx
index 8c0ed789c..3f8513573 100644
--- a/src/windows/SerialPortWINDOWS.hxx
+++ b/src/windows/SerialPortWINDOWS.hxx
@@ -47,6 +47,14 @@ class SerialPortWINDOWS : public SerialPort
     */
     bool writeByte(uInt8 data) override;
 
+    /**
+      Test for 'Clear To Send' enabled.  By default, assume it's always
+      OK to send more data.
+
+      @return  True if CTS signal enabled, else false
+    */
+    bool isCTS() override;
+
   private:
     // Handle to serial port
     HANDLE myHandle{0};
diff --git a/src/windows/Stella.vcxproj b/src/windows/Stella.vcxproj
index c6ba9d7ff..52a8c4327 100644
--- a/src/windows/Stella.vcxproj
+++ b/src/windows/Stella.vcxproj
@@ -1774,6 +1774,7 @@
     <ClInclude Include="..\emucore\MindLink.hxx" />
     <ClInclude Include="..\emucore\PointingDevice.hxx" />
     <ClInclude Include="..\emucore\ProfilingRunner.hxx" />
+    <ClInclude Include="..\emucore\SerialPort.hxx" />
     <ClInclude Include="..\emucore\TIASurface.hxx" />
     <ClInclude Include="..\emucore\tia\Audio.hxx" />
     <ClInclude Include="..\emucore\tia\AudioChannel.hxx" />
diff --git a/src/windows/Stella.vcxproj.filters b/src/windows/Stella.vcxproj.filters
index 215e9eeab..5875efb8c 100644
--- a/src/windows/Stella.vcxproj.filters
+++ b/src/windows/Stella.vcxproj.filters
@@ -2087,6 +2087,9 @@
     <ClInclude Include="..\gui\WhatsNewDialog.hxx">
       <Filter>Header Files\gui</Filter>
     </ClInclude>
+    <ClInclude Include="..\emucore\SerialPort.hxx">
+      <Filter>Header Files\emucore</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <None Include="stella.ico">