diff --git a/implementations/rust/preserves-tools/src/bin/preserves-tool.rs b/implementations/rust/preserves-tools/src/bin/preserves-tool.rs
index dcac6a2..9c9cf3f 100644
--- a/implementations/rust/preserves-tools/src/bin/preserves-tool.rs
+++ b/implementations/rust/preserves-tools/src/bin/preserves-tool.rs
@@ -283,7 +283,7 @@ impl<R: io::Read> io::Read for RollingBuffer<R> {
                 }
                 continue;
             }
-            &buf[.. n].copy_from_slice(&self.buf[i .. i + n]);
+            let _ = &buf[.. n].copy_from_slice(&self.buf[i .. i + n]);
             self.pos += n;
             return Ok(n);
         }