diff --git a/src/histogram_const.rs b/src/histogram_const.rs
index e78e61a..466fd7e 100644
--- a/src/histogram_const.rs
+++ b/src/histogram_const.rs
@@ -197,6 +197,7 @@ where [u8; LEN + 1]: Sized {
 }
 
 /// Iterate over all `(range, count)` pairs in the histogram.
+#[derive(Clone, Debug)]
 pub struct IterHistogram<'a> {
     remaining_bin: &'a [u64],
     remaining_range: &'a [f64],
@@ -281,6 +282,7 @@ fn multinomal_variance(n: f64, n_tot_inv: f64) -> f64 {
 }
 
 /// Iterate over the bins normalized by bin width.
+#[derive(Clone, Debug)]
 pub struct IterNormalized<T>
     where T: Iterator<Item = ((f64, f64), u64)>
 {
@@ -299,6 +301,7 @@ impl<T> Iterator for IterNormalized<T>
 }
 
 /// Iterate over the widths of the bins.
+#[derive(Clone, Debug)]
 pub struct IterWidths<T>
     where T: Iterator<Item = ((f64, f64), u64)>
 {
@@ -317,6 +320,7 @@ impl<T> Iterator for IterWidths<T>
 }
 
 /// Iterate over the bin centers.
+#[derive(Clone, Debug)]
 pub struct IterBinCenters<T>
     where T: Iterator<Item = ((f64, f64), u64)>
 {
@@ -335,6 +339,7 @@ impl<T> Iterator for IterBinCenters<T>
 }
 
 /// Iterate over the variances.
+#[derive(Clone, Debug)]
 pub struct IterVariances<T>
     where T: Iterator<Item = ((f64, f64), u64)>
 {
@@ -352,4 +357,4 @@ impl<T> Iterator for IterVariances<T>
         self.histogram_iter.next()
             .map(|(_, n)| multinomal_variance(n as f64, self.sum_inv))
     }
-}
\ No newline at end of file
+}
diff --git a/tests/integration/histogram_const.rs b/tests/integration/histogram_const.rs
index 9627e03..c5d5869 100644
--- a/tests/integration/histogram_const.rs
+++ b/tests/integration/histogram_const.rs
@@ -4,7 +4,7 @@ use rand_distr::Distribution;
 
 use average::{Merge, assert_almost_eq};
 use average::histogram_const::{Histogram, InvalidRangeError,
-SampleOutOfRangeError};
+    SampleOutOfRangeError};
 
 type Histogram10 = Histogram<10>;