Disable nightly-only tests on non nightly compiler
diff --git a/tests/test_generics.rs b/tests/test_generics.rs
index 1bd15f3..74771d5 100644
--- a/tests/test_generics.rs
+++ b/tests/test_generics.rs
@@ -1,3 +1,4 @@
+#![cfg(not(syn_disable_nightly_tests))]
 #![recursion_limit = "1024"]
 #![feature(rustc_private)]