diff -r b99b41325d89 -r 50677f43ac3d make/autoconf/platform.m4
--- a/make/autoconf/platform.m4	Tue Jan 01 20:09:02 2019 -0500
+++ b/make/autoconf/platform.m4	Wed Jan 02 12:59:26 2019 +0100
@@ -188,6 +188,10 @@
       VAR_OS=windows
       VAR_OS_ENV=windows.cygwin
       ;;
+    *wsl*)
+      VAR_OS=windows
+      VAR_OS_ENV=windows.wsl
+      ;;
     *mingw*)
       VAR_OS=windows
       VAR_OS_ENV=windows.msys