diff --git a/defs.h b/defs.h
index 2a6c47a..1adbf78 100644
--- a/defs.h
+++ b/defs.h
@@ -174,6 +174,7 @@ void            usertrapret(void);
 void            uartinit(void);
 void            uartintr(void);
 void            uartputc(int);
+int             uartgetc(void);
 
 // vm.c
 void            kvminit(void);
diff --git a/uart.c b/uart.c
index 659c574..b6271c1 100644
--- a/uart.c
+++ b/uart.c
@@ -49,11 +49,15 @@ uartputc(int c)
   *R(0) = c;
 }
 
-uint
+int
 uartgetc(void)
 {
-  // XXX this isn't right, must check there's data in the FIFO.
-  return *R(0);
+  if(*(5) & 0x01){
+    // input data is ready.
+    return *R(0);
+  } else {
+    return -1;
+  };
 }
 
 void