diff --git a/histogram.iternal.h b/histogram.iternal.h
index 0698c96..f09dda6 100644
--- a/histogram.iternal.h
+++ b/histogram.iternal.h
@@ -1,8 +1,8 @@
-#ifndef HISTOGRAM_INTERNAL_H_INCLUDED
-#define HISTOGRAM_INTERNAL_H_INCLUDED
-
-#include <vector>
-
-bool find_minmax(const std::vector<double>& numbers, double& min, double& max);
-
-#endif
+#ifndef HISTOGRAM_ITERNAL_H_INCLUDED
+#define HISTOGRAM_ITERNAL_H_INCLUDED
+
+#include <vector>
+
+bool find_minmax(const std::vector<double>& numbers, double& min, double& max);
+
+#endif