diff --git a/src/average_median/average_median.h b/src/average_median/average_median.h
index 8b13789..b9d773f 100644
--- a/src/average_median/average_median.h
+++ b/src/average_median/average_median.h
@@ -1 +1,9 @@
+#ifndef average_median_H
+#define average_median_H
+
+double average(const double *data, int n);
+double median(double *data, int n);
+
+#endif
+