diff --git a/include/libp2p/crypto/key.h b/include/libp2p/crypto/key.h
index 1139785..245b9e8 100644
--- a/include/libp2p/crypto/key.h
+++ b/include/libp2p/crypto/key.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdlib.h>
+
 /**
  * Utilities for public keys
  */