diff --git a/src/idxsets/idxrange.rs b/src/idxsets/idxrange.rs
index ea19299..9d22360 100644
--- a/src/idxsets/idxrange.rs
+++ b/src/idxsets/idxrange.rs
@@ -28,11 +28,42 @@ impl IdxSet for IdxRange {
     }
 
     fn size(&self) -> usize {
-        ((self.0.end - 1) / crate::bits::bitfield::BITS + 1)
-            - self.0.start / crate::bits::bitfield::BITS
+        if self.0.end <= self.0.start {
+            0
+        } else {
+            let bitfield_end = (self.0.end - 1) / crate::bits::bitfield::BITS + 1;
+            let bitfield_start = self.0.start / crate::bits::bitfield::BITS;
+            bitfield_end - bitfield_start
+        }
     }
 
     fn intersect(&self, idx: &Bitfield) -> Bitfield {
         (*idx).clip(&self.0)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_size_of_zero_length_idxrange() {
+        let zero_range = IdxRange(0..0);
+
+        assert_eq!(zero_range.size(), 0);
+    }
+
+    #[test]
+    fn test_size_of_single_length_idxrange() {
+        let zero_range = IdxRange(0..1);
+
+        assert_eq!(zero_range.size(), 1);
+    }
+
+    #[test]
+    fn test_size_of_short_idxrange() {
+        let zero_range = IdxRange(0..7);
+
+        assert_eq!(zero_range.size(), 1);
+    }
+}
diff --git a/src/types/entry.rs b/src/types/entry.rs
index 10e09e3..aee8fa5 100644
--- a/src/types/entry.rs
+++ b/src/types/entry.rs
@@ -95,12 +95,8 @@ where
     where
         R: Debug,
     {
-        self.get().or_else(|| {
-            panic!(format!(
-                "retriever: Entry::or_panic(): {:?} doesn't exist",
-                &self.id
-            ))
-        });
+        self.get()
+            .or_else(|| panic!("retriever: Entry::or_panic(): {:?} doesn't exist", &self.id));
 
         self
     }