diff --git a/histogram.cpp b/histogram.cpp
index 534f64c..9eec184 100644
--- a/histogram.cpp
+++ b/histogram.cpp
@@ -4,7 +4,7 @@
 #include "histogram.h"
 using namespace std;
 
-static void find_minmax(const vector<double>& numbers, double& min, double& max) {
+void find_minmax(const vector<double>& numbers, double& min, double& max) {
     min = numbers[0];
     max = numbers[0];
     for (double x : numbers)
diff --git a/histogram_internal.h b/histogram_internal.h
new file mode 100644
index 0000000..3fb3176
--- /dev/null
+++ b/histogram_internal.h
@@ -0,0 +1,4 @@
+#pragma once
+#include <vector>
+
+void find_minmax(const std::vector<double>& numbers, double& min, double& max);
\ No newline at end of file