diff --git a/roaring/src/bitmap/store/bitmap_store.rs b/roaring/src/bitmap/store/bitmap_store.rs
index a60f3a1a..ceaeb5c2 100644
--- a/roaring/src/bitmap/store/bitmap_store.rs
+++ b/roaring/src/bitmap/store/bitmap_store.rs
@@ -403,9 +403,9 @@ impl Display for Error {
 impl std::error::Error for Error {}
 
 pub struct BitmapIter<B: Borrow<[u64; BITMAP_LENGTH]>> {
-    key: usize,
+    key: u16,
     value: u64,
-    key_back: usize,
+    key_back: u16,
     value_back: u64,
     bits: B,
 }
@@ -415,7 +415,7 @@ impl<B: Borrow<[u64; BITMAP_LENGTH]>> BitmapIter<B> {
         BitmapIter {
             key: 0,
             value: bits.borrow()[0],
-            key_back: BITMAP_LENGTH - 1,
+            key_back: BITMAP_LENGTH as u16 - 1,
             value_back: bits.borrow()[BITMAP_LENGTH - 1],
             bits,
         }
@@ -432,7 +432,7 @@ impl<B: Borrow<[u64; BITMAP_LENGTH]>> Iterator for BitmapIter<B> {
                     return None;
                 }
                 for key in self.key + 1..self.key_back {
-                    self.value = unsafe { *self.bits.borrow().get_unchecked(key) };
+                    self.value = unsafe { *self.bits.borrow().get_unchecked(key as usize) };
                     if self.value != 0 {
                         self.key = key;
                         break 'get_val;
@@ -445,9 +445,9 @@ impl<B: Borrow<[u64; BITMAP_LENGTH]>> Iterator for BitmapIter<B> {
                 }
             }
         }
-        let index = self.value.trailing_zeros() as usize;
+        let index = self.value.trailing_zeros() as u16;
         self.value &= self.value - 1;
-        Some((64 * self.key + index) as u16)
+        Some(64 * self.key + index)
     }
 }
 
@@ -461,13 +461,14 @@ impl<B: Borrow<[u64; BITMAP_LENGTH]>> DoubleEndedIterator for BitmapIter<B> {
                     return None;
                 }
                 self.key_back -= 1;
-                self.value_back = unsafe { *self.bits.borrow().get_unchecked(self.key_back) };
+                self.value_back =
+                    unsafe { *self.bits.borrow().get_unchecked(self.key_back as usize) };
                 continue;
             }
-            let index_from_left = value.leading_zeros() as usize;
+            let index_from_left = value.leading_zeros() as u16;
             let index = 63 - index_from_left;
             *value &= !(1 << index);
-            return Some((64 * self.key_back + index) as u16);
+            return Some(64 * self.key_back + index);
         }
     }
 }