diff --git a/compiler/rustc_target/src/spec/avr_gnu_base.rs b/compiler/rustc_target/src/spec/avr_gnu_base.rs
index ff559c2bfd684..527a322d56a4f 100644
--- a/compiler/rustc_target/src/spec/avr_gnu_base.rs
+++ b/compiler/rustc_target/src/spec/avr_gnu_base.rs
@@ -45,6 +45,8 @@ pub fn target(target_cpu: String) -> TargetResult {
             late_link_args: vec![(LinkerFlavor::Gcc, vec!["-lgcc".to_owned()])]
                 .into_iter()
                 .collect(),
+            max_atomic_width: Some(0),
+            atomic_cas: false,
             ..TargetOptions::default()
         },
     })