diff --git a/beginner/apps/src/bin/radio-puzzle-3.rs b/beginner/apps/src/bin/radio-puzzle-3.rs
index 10529f4..a5041ae 100644
--- a/beginner/apps/src/bin/radio-puzzle-3.rs
+++ b/beginner/apps/src/bin/radio-puzzle-3.rs
@@ -20,7 +20,7 @@ fn main() -> ! {
     radio.set_channel(Channel::_25);
 
     // capacity (128) should be large enough for the ASCII range
-    let mut dict = LinearMap::<u8, u8, 128>::new();
+    let dict = LinearMap::<u8, u8, 128>::new();
 
     let mut packet = Packet::new();
     // TODO do the whole ASCII range [0, 127]