diff --git a/src/prim/wasi/prim.c b/src/prim/wasi/prim.c
index 50511f0b..891c7123 100644
--- a/src/prim/wasi/prim.c
+++ b/src/prim/wasi/prim.c
@@ -40,6 +40,7 @@ int _mi_prim_free(void* addr, size_t size ) {
 //---------------------------------------------
 
 #if defined(MI_USE_SBRK)
+  #include <unistd.h>
   static void* mi_memory_grow( size_t size ) {
     void* p = sbrk(size);
     if (p == (void*)(-1)) return NULL;