diff --git a/Objects/mimalloc/prim/wasi/prim.c b/Objects/mimalloc/prim/wasi/prim.c
index 25e64fa3c40bf5..640dac0493f573 100644
--- a/Objects/mimalloc/prim/wasi/prim.c
+++ b/Objects/mimalloc/prim/wasi/prim.c
@@ -11,6 +11,7 @@ terms of the MIT license. A copy of the license can be found in the file
 #include "mimalloc/internal.h"
 #include "mimalloc/atomic.h"
 #include "mimalloc/prim.h"
+#include <unistd.h>               // sbrk()
 
 //---------------------------------------------
 // Initialize