diff --git a/src/histogram.rs b/src/histogram.rs
index 14daa40..53e7556 100644
--- a/src/histogram.rs
+++ b/src/histogram.rs
@@ -4,6 +4,8 @@
 /// module with the given name. This includes the `Histogram` struct, the number
 /// of bins `LEN` and the histogram iterator `HistogramIter`.
 ///
+/// Note that you need to make sure that `core` is accessible to the macro.
+///
 ///
 /// # Example
 ///