diff --git a/histogram_internal.h b/histogram_internal.h
deleted file mode 100644
index 7d546c7..0000000
--- a/histogram_internal.h
+++ /dev/null
@@ -1,10 +0,0 @@
-#ifndef HISTOGRAM_INTERNAL_H_INCLUDED
-#define HISTOGRAM_INTERNAL_H_INCLUDED
-#include <vector>
-#include <string>
-
-bool find_minmax(const std::vector<double>& numbers, double& min, double& max);
-
-std::string
-bin_color(size_t bin, size_t max_count);
-#endif // HISTOGRAM_INTERNAL_H_INCLUDED