diff --git a/srcpkgs/ctwm/template b/srcpkgs/ctwm/template
index 938e2bc5313..5746acec975 100644
--- a/srcpkgs/ctwm/template
+++ b/srcpkgs/ctwm/template
@@ -1,7 +1,7 @@
 # Template file for 'ctwm'
 pkgname=ctwm
 version=4.0.3
-revision=1
+revision=2
 build_style=cmake
 configure_args="
 	-DUSE_M4=$(vopt_if m4 ON OFF)
@@ -19,6 +19,7 @@ license="MIT"
 homepage="https://ctwm.org"
 distfiles="https://ctwm.org/dist/ctwm-${version}.tar.xz"
 checksum=2e4b475a0168cb799723fd693b359e188179e51ce476ab453689db8fcdfc800c
+CFLAGS="-D_GNU_SOURCE"
 
 build_options="m4 xpm jpeg ewmh rplay xrandr"
 build_options_default="m4 xpm ewmh xrandr"