diff --git a/pkgs/build-support/lib/cmake.nix b/pkgs/build-support/lib/cmake.nix
index 796f69235475..f495f3d1d6bf 100644
--- a/pkgs/build-support/lib/cmake.nix
+++ b/pkgs/build-support/lib/cmake.nix
@@ -12,7 +12,9 @@ let
     [
       "-DCMAKE_SYSTEM_NAME=${
         findFirst isString "Generic" (
-          optional (!stdenv.hostPlatform.isRedox) stdenv.hostPlatform.uname.system
+          # uname -s is CYGWIN_NT[...] on cygwin, but cmake expects CYGWIN
+          optional (stdenv.hostPlatform.isCygwin) "CYGWIN"
+          ++ optional (!stdenv.hostPlatform.isRedox) stdenv.hostPlatform.uname.system
         )
       }"
     ]