diff --git a/pkgs/by-name/ef/efitools/package.nix b/pkgs/by-name/ef/efitools/package.nix
index 8f793128f4be..5248199c6873 100644
--- a/pkgs/by-name/ef/efitools/package.nix
+++ b/pkgs/by-name/ef/efitools/package.nix
@@ -39,6 +39,7 @@ stdenv.mkDerivation rec {
     sed -i -e 's#/usr/include/efi#${gnu-efi}/include/efi/#g' Make.rules
     sed -i -e 's#/usr/lib64/gnuefi#${gnu-efi}/lib/#g' Make.rules
     sed -i -e 's#$(DESTDIR)/usr#$(out)#g' Make.rules
+    sed -i '$asign-efi-sig-list.o flash-var.o: CFLAGS += -D_GNU_SOURCE' Makefile
     substituteInPlace lib/console.c --replace "EFI_WARN_UNKOWN_GLYPH" "EFI_WARN_UNKNOWN_GLYPH"
     patchShebangs .
   '';