diff --git a/src/assert.cc b/src/assert.cc
index 018567da..74b939a4 100644
--- a/src/assert.cc
+++ b/src/assert.cc
@@ -9,6 +9,7 @@
 
 #include <sys/types.h>
 #include <unistd.h>
+#include <stdlib.h>
 
 namespace Kakoune
 {