diff --git a/crates/testkit/src/sweep.rs b/crates/testkit/src/sweep.rs
index ae3552226e..863a5c9029 100644
--- a/crates/testkit/src/sweep.rs
+++ b/crates/testkit/src/sweep.rs
@@ -20,10 +20,11 @@ impl Sweep {
         }
         let parts = parts.max(1);
         let part = match std::env::var("PHOTOCRAFT_SWEEP_PART") {
-            Ok(v) => match v.parse::<u64>() {
-                Ok(p) if p < parts => p,
-                _ => panic!("PHOTOCRAFT_SWEEP_PART={v:?} is not a part number below {parts}"),
-            },
+            Ok(v) => {
+                let p = v.parse::<u64>().unwrap_or(u64::MAX);
+                assert!(p < parts, "PHOTOCRAFT_SWEEP_PART={v:?} is not a part number below {parts}");
+                p
+            }
             Err(_) => SystemTime::now().duration_since(UNIX_EPOCH).map(|d| d.as_secs() / 86_400).unwrap_or_default() % parts,
         };
         eprintln!("sweep part {part} of {parts}: replay with PHOTOCRAFT_SWEEP_PART={part}, run every part with PHOTOCRAFT_FULL_SWEEP=1");