diff --git a/histogram.cpp b/histogram.cpp
index f23db86..45c959d 100644
--- a/histogram.cpp
+++ b/histogram.cpp
@@ -3,7 +3,7 @@
 #include "histogram.h"
 using namespace std;
 
-void
+bool
 find_minmax(const vector<double>& numbers, double& min, double& max) {
     min = numbers[0];
     for (size_t i = 1; i < numbers.size(); i++) {
diff --git a/histogram_internal.h b/histogram_internal.h
index 8179497..a512ac6 100644
--- a/histogram_internal.h
+++ b/histogram_internal.h
@@ -2,5 +2,5 @@
 
 #include <vector>
 
-void
+bool
 find_minmax(const std::vector<double>& numbers, double& min, double& max);