diff --git a/histogram_internal.h b/histogram_internal.h
index ee7778f..0a08577 100644
--- a/histogram_internal.h
+++ b/histogram_internal.h
@@ -3,8 +3,8 @@
 
 #include <vector>
 
-std::vector<size_t>
-find_minmax(const std::vector<double>& numbers, double& min, double& max);
+
+void find_minmax(const std::vector<double>& numbers, double& min, double& max);
 
 
 #endif // HISTOGRAM_INTERNAL_H_INCLUDED