diff --git a/tests/snippets/builtin_ascii.py b/tests/snippets/builtin_ascii.py
index 694c1916c..2132723c6 100644
--- a/tests/snippets/builtin_ascii.py
+++ b/tests/snippets/builtin_ascii.py
@@ -1,4 +1,7 @@
 assert ascii('hello world') == "'hello world'"
 assert ascii('안녕 세상') == "'\\uc548\\ub155 \\uc138\\uc0c1'"
 assert ascii('안녕 RustPython') == "'\\uc548\\ub155 RustPython'"
-assert ascii(5) == '5'
\ No newline at end of file
+assert ascii(5) == '5'
+assert ascii(chr(0x10001)) == "'\\U00010001'"
+assert ascii(chr(0x9999)) == "'\\u9999'"
+assert ascii(chr(0x0A)) == "'\\n'"
\ No newline at end of file
diff --git a/vm/src/builtins.rs b/vm/src/builtins.rs
index 0affb002d..a6a041a00 100644
--- a/vm/src/builtins.rs
+++ b/vm/src/builtins.rs
@@ -66,7 +66,12 @@ fn builtin_ascii(obj: PyObjectRef, vm: &VirtualMachine) -> PyResult<String> {
         if c.is_ascii() {
             ascii.push(c)
         } else {
-            let hex = format!("\\u{:x}", c as i64);
+            let c = c as i64;
+            let hex = if c < 0x10000 {
+                format!("\\u{:04x}", c)
+            } else {
+                format!("\\U{:08x}", c)
+            };
             ascii.push_str(&hex)
         }
     }