diff --git a/pkgs/swconfig/default.nix b/pkgs/swconfig/default.nix
index dd91056..c706746 100644
--- a/pkgs/swconfig/default.nix
+++ b/pkgs/swconfig/default.nix
@@ -27,6 +27,7 @@ stdenv.mkDerivation {
   patchPhase = ''
     mkdir -p from_kernel/linux
     cp ${switchDotH} from_kernel/linux/switch.h
+    sed -i '1i #include <ctype.h>'  swlib.c
   '';
 
   buildPhase = ''