diff --git a/tools/gn/args.cc b/tools/gn/args.cc
index 823a8cc..581c8ac 100644
--- a/tools/gn/args.cc
+++ b/tools/gn/args.cc
@@ -258,6 +258,8 @@
   os = "linux";
 #elif defined(OS_ANDROID)
   os = "android";
+#elif defined(OS_NETBSD)
+  os = "netbsd";
 #else
   #error Unknown OS type.
 #endif