diff --git a/shell.nix b/shell.nix
index 7814a10d1..6cfda2da9 100644
--- a/shell.nix
+++ b/shell.nix
@@ -86,6 +86,6 @@ mkShell {
   shellHook = ''
     # Prevent the avr-gcc wrapper from picking up host GCC flags
     # like -iframework, which is problematic on Darwin
-    unset NIX_TARGET_CFLAGS_COMPILE
+    unset NIX_CFLAGS_COMPILE_FOR_TARGET
   '';
 }