diff --git a/histogram.cpp b/histogram.cpp
index b91f450..898675d 100644
--- a/histogram.cpp
+++ b/histogram.cpp
@@ -1,8 +1,12 @@
 #include "histogram.h"
+#include "histogram_internal.h"
 
 using namespace std;
 
-void find_minmax(const vector<double>& numbers, double& min, double& max) {
+bool find_minmax(const vector<double>& numbers, double& min, double& max) {
+    if (numbers.size() == 0) {
+        return false;
+    }
     min = numbers[0];
     max = numbers[0];
     for (double x : numbers) {
@@ -13,6 +17,7 @@ void find_minmax(const vector<double>& numbers, double& min, double& max) {
             max = x;
         }
     }
+    return true;
 }
 vector<size_t> make_histogram(const vector<double> &numbers, size_t bin_count) {
     vector<size_t> bins(bin_count);