diff --git a/histogram.cpp b/histogram.cpp
index 4c759c6..0c26cb0 100644
--- a/histogram.cpp
+++ b/histogram.cpp
@@ -3,7 +3,7 @@
 #include <iostream>
 using namespace std;
 
-void
+static void
 find_minmax(const vector<double>& numbers, double& min, double& max) {
     min = numbers[0];
     max = numbers[0];