diff --git a/toxcore/mono_time.c b/toxcore/mono_time.c
index 2a2ec3a284..88017135f4 100644
--- a/toxcore/mono_time.c
+++ b/toxcore/mono_time.c
@@ -26,6 +26,7 @@
 #include <sys/time.h>
 #endif
 
+#include <assert.h>
 #include <pthread.h>
 #include <stdlib.h>
 #include <time.h>