diff --git a/src/main/java/com/ghgande/j2mod/modbus/io/ModbusSerialTransport.java b/src/main/java/com/ghgande/j2mod/modbus/io/ModbusSerialTransport.java
index 7abd4cf..4007d24 100644
--- a/src/main/java/com/ghgande/j2mod/modbus/io/ModbusSerialTransport.java
+++ b/src/main/java/com/ghgande/j2mod/modbus/io/ModbusSerialTransport.java
@@ -61,7 +61,7 @@ public abstract class ModbusSerialTransport extends AbstractModbusTransport {
     /**
      * The number of nanoseconds there is in a second
      */
-    private static final int NS_IN_A_SEC = 1_000_000_000;
+    private static final double NS_IN_A_SEC = 1_000_000_000D;
 
     private static final String CANNOT_READ_FROM_SERIAL_PORT = "Cannot read from serial port";
     private static final String COMM_PORT_IS_NOT_VALID_OR_NOT_OPEN = "Comm port is not valid or not open";