diff --git a/dsp/src/iir.rs b/dsp/src/iir.rs
index f58fb64..04d7c8e 100644
--- a/dsp/src/iir.rs
+++ b/dsp/src/iir.rs
@@ -164,7 +164,8 @@ impl IIR {
         // `xy` contains       x0 x1 y0 y1 y2
         // Increment time      x1 x2 y1 y2 y3
         // Shift               x1 x1 x2 y1 y2
-        xy.copy_within(0..n - 1, 1);  // unrolls better than xy.rotate_right(1)
+        // This unrolls better than xy.rotate_right(1)
+        xy.copy_within(0..n - 1, 1);
         // Store x0            x0 x1 x2 y1 y2
         xy[0] = x0;
         // Compute y0 by multiply-accumulate