diff --git a/croaring/src/treemap/iter.rs b/croaring/src/treemap/iter.rs
index d25504a..f339fc5 100644
--- a/croaring/src/treemap/iter.rs
+++ b/croaring/src/treemap/iter.rs
@@ -17,10 +17,11 @@ impl<'a> Iterator for To64Iter<'a> {
     }
 }
 
-fn to64iter<'a>(t: (&'a u32, &'a Bitmap)) -> To64Iter<'a> {
+fn to64iter<'a>((key, bitmap): (&'a u32, &'a Bitmap)) -> To64Iter<'a> {
+    assert!(!bitmap.is_empty(), "empty bitmap at {key}");
     To64Iter {
-        key: *t.0,
-        iterator: t.1.iter(),
+        key: *key,
+        iterator: bitmap.iter(),
     }
 }
 
diff --git a/fuzz/fuzz_targets/arbitrary_ops64/mod.rs b/fuzz/fuzz_targets/arbitrary_ops64/mod.rs
index c923ae2..47b31d9 100644
--- a/fuzz/fuzz_targets/arbitrary_ops64/mod.rs
+++ b/fuzz/fuzz_targets/arbitrary_ops64/mod.rs
@@ -417,7 +417,7 @@ pub fn assert_64_eq(lhs: &Bitmap64, rhs: &Treemap) {
             let r = rhs.next().unwrap();
             assert_eq!(l, r, "{l} != {r} at {i}");
         }
-        assert!(rhs.next().is_none());
+        assert_eq!(rhs.next(), None);
         panic!("Serialize not equal, but all items equal?")
     }
 }