diff --git a/crates/nu-command/src/strings/str_/case/downcase.rs b/crates/nu-command/src/strings/str_/case/downcase.rs
index 3918689deac9..a5984ffc9a3b 100644
--- a/crates/nu-command/src/strings/str_/case/downcase.rs
+++ b/crates/nu-command/src/strings/str_/case/downcase.rs
@@ -121,7 +121,7 @@ fn operate(
 
 fn action(input: &Value, head: Span) -> Value {
     match input {
-        Value::String { val, .. } => Value::string(val.to_ascii_lowercase(), head),
+        Value::String { val, .. } => Value::string(val.to_lowercase(), head),
         Value::Error { .. } => input.clone(),
         _ => Value::error(
             ShellError::OnlySupportsThisInputType {
diff --git a/crates/nu-command/tests/commands/str_/mod.rs b/crates/nu-command/tests/commands/str_/mod.rs
index 5e136b40b8c0..382f2bf20fe9 100644
--- a/crates/nu-command/tests/commands/str_/mod.rs
+++ b/crates/nu-command/tests/commands/str_/mod.rs
@@ -76,6 +76,13 @@ fn downcases() {
     })
 }
 
+#[test]
+fn non_ascii_downcase() {
+    let actual = nu!("'ὈΔΥΣΣΕΎΣ' | str downcase");
+
+    assert_eq!(actual.out, "ὀδυσσεύς");
+}
+
 #[test]
 fn upcases() {
     Playground::setup("str_test_4", |dirs, sandbox| {
@@ -96,6 +103,13 @@ fn upcases() {
     })
 }
 
+#[test]
+fn non_ascii_upcase() {
+    let actual = nu!("'ὀδυσσεύς' | str upcase");
+
+    assert_eq!(actual.out, "ὈΔΥΣΣΕΎΣ");
+}
+
 #[test]
 #[ignore = "Playgrounds are not supported in nu-cmd-extra"]
 fn camelcases() {