diff --git a/src/lib.rs b/src/lib.rs
index 2e02c3a..7af1dc9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -249,12 +249,12 @@ fn decode(filename: &str) -> PyResult<PyFrameIterator> {
 pub fn decode_to_files(filename: &str, frames_root: &str) -> anyhow::Result<()> {
     let frameiter = Decoder::new(filename)?;
     for (i, frame) in frameiter.enumerate() {
-        let name = format!("{}/{:04}.png", frames_root, i);
+        let name = format!("{}/{:05}.png", frames_root, i);
         if let Err(_e) = write_raw_frame(&name, &frame.raw) {
             println!("skipping bad frame {}", i);
             continue;
         }
-        let name = format!("{}/temp_{:04}.png", frames_root, i);
+        let name = format!("{}/temp_{:05}.png", frames_root, i);
         let pixels = frame.pixels();
         write_calibrated_frame(&name, &pixels)?;
     }