diff --git a/Rust/rustifinity/challenges/mutable-references.rs b/Rust/rustifinity/challenges/mutable-references.rs
new file mode 100644
index 0000000..c3b7e10
--- /dev/null
+++ b/Rust/rustifinity/challenges/mutable-references.rs
@@ -0,0 +1,4 @@
+pub fn append_suffix(s: &mut String, suffix: &str) {
+    // Your code here...
+    s.push_str(suffix);
+}