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)]
diff --git a/tests/test_grouping.rs b/tests/test_grouping.rs
index 887ac48..a2357e9 100644
--- a/tests/test_grouping.rs
+++ b/tests/test_grouping.rs
@@ -1,3 +1,4 @@
+#![cfg(not(syn_disable_nightly_tests))]
#![recursion_limit = "1024"]
#![feature(rustc_private)]
diff --git a/tests/test_precedence.rs b/tests/test_precedence.rs
index 71017b6..f516b40 100644
--- a/tests/test_precedence.rs
+++ b/tests/test_precedence.rs
@@ -1,3 +1,4 @@
+#![cfg(not(syn_disable_nightly_tests))]
#![recursion_limit = "1024"]
#![feature(rustc_private)]
diff --git a/tests/test_round_trip.rs b/tests/test_round_trip.rs
index 4c7886a..bf1ee1c 100644
--- a/tests/test_round_trip.rs
+++ b/tests/test_round_trip.rs
@@ -1,3 +1,4 @@
+#![cfg(not(syn_disable_nightly_tests))]
#![recursion_limit = "1024"]
#![feature(rustc_private)]