diff --git a/Sources/SwiftSerial.swift b/Sources/SwiftSerial.swift
index fdeb067..71002b9 100644
--- a/Sources/SwiftSerial.swift
+++ b/Sources/SwiftSerial.swift
@@ -383,13 +383,15 @@ public class SerialPort {
             }
             dtrState = value
             var flags = TIOCM_DTR
-            ioctl(fileDescriptor, dtrState ? TIOCMBIS : TIOCMBIC, &flags)
+            if(ioctl(fileDescriptor, UInt(dtrState ? TIOCMBIS : TIOCMBIC), &flags) != 0){
+                print("Failed to apply dtr")
+            }
         }
     }
     
     public var inWaiting: Int {
         get{
-            return Int(ioctl(fileDescriptor!, FIONREAD))
+            return Int(ioctl(fileDescriptor!, UInt(FIONREAD)))
         }
     }
 }