diff --git a/day4/d4p2.go b/day4/d4p2.go
index c5c4ddd..026d29f 100644
--- a/day4/d4p2.go
+++ b/day4/d4p2.go
@@ -1,4 +1,3 @@
-// +build linux
 package main
 
 import (
@@ -8,6 +7,7 @@ import (
     "os"
     "strings"
     "regexp"
+    "runtime"
 )
 
 func find_num_wins(winners string, numbers string) int {
@@ -24,6 +24,10 @@ func find_num_wins(winners string, numbers string) int {
 
 
 func main() {
+    if runtime.GOOS != "linux" {
+        panic("This is for Linux only.")
+    }
+
     if len(os.Args) < 2 {
         panic("You did not specify an input file.")
     }