diff --git a/build.rs b/build.rs
index 24160e201..eaa188fa1 100644
--- a/build.rs
+++ b/build.rs
@@ -1,12 +1,16 @@
+use std::env;
+
 fn main() {
-    if cfg!(windows) {
+    if env::var("CARGO_CFG_WINDOWS").is_ok() {
         // The first choice is Windows because DXGI is amazing.
         println!("cargo:rustc-cfg=dxgi");
-    } else if cfg!(target_os="macos") {
+    } else if env::var("CARGO_CFG_TARGET_OS").unwrap() == "macos" {
         // Quartz is second because macOS is the (annoying) exception.
         println!("cargo:rustc-cfg=quartz");
-    } else if cfg!(unix) {
+    } else if env::var("CARGO_CFG_UNIX").is_ok() {
         // On UNIX we pray that X11 (with XCB) is available.
         println!("cargo:rustc-cfg=x11");
+    } else {
+        panic!("Platform not supported");
     }
 }