diff --git a/library/kani_macros/Cargo.toml b/library/kani_macros/Cargo.toml
index a1aeb743952b..6930366b84fc 100644
--- a/library/kani_macros/Cargo.toml
+++ b/library/kani_macros/Cargo.toml
@@ -13,7 +13,7 @@ proc-macro = true
 
 [dependencies]
 proc-macro2 = "1.0"
-proc-macro-error2 = "2.0.0"
+proc-macro-error2 = { version = "2.0.0", features = ["nightly"] }
 quote = "1.0.20"
 syn = { version = "2.0.18", features = ["full", "visit-mut", "visit", "extra-traits"] }
 
diff --git a/tests/ui/derive-arbitrary/union/expected b/tests/ui/derive-arbitrary/union/expected
index e54592a47ca6..3acea286d7ca 100644
--- a/tests/ui/derive-arbitrary/union/expected
+++ b/tests/ui/derive-arbitrary/union/expected
@@ -3,7 +3,10 @@ error: Cannot derive `Arbitrary` for `Wrapper` union
 |\
 | #[derive(kani::Arbitrary)]\
 |          ^^^^^^^^^^^^^^^\
-|
+|\
 note: `#[derive(Arbitrary)]` cannot be used for unions such as `Wrapper`
 
+|\
+| union Wrapper {\
+|       ^^^^^^^\
 = note: this error originates in the derive macro `kani::Arbitrary`