diff --git a/histogram_internal.h b/histogram_internal.h
index 616921d..a4eddaa 100644
--- a/histogram_internal.h
+++ b/histogram_internal.h
@@ -3,6 +3,6 @@
 
 #include <vector>
 
-void 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