diff --git a/system/lib/dlmalloc.c b/system/lib/dlmalloc.c
--- a/system/lib/dlmalloc.c
+++ b/system/lib/dlmalloc.c
@@ -1564,7 +1564,8 @@ size_t bulk_free(void**, size_t n_elements) __attribute__((weak, alias("dlbulk_f
 #endif /* LACKS_FCNTL_H */
 #endif /* HAVE_MMAP */
 #ifndef LACKS_UNISTD_H
-#include <unistd.h>     /* for sbrk, sysconf */
+// #include <unistd.h>     /* for sbrk, sysconf */
+extern void*     sbrk(ptrdiff_t);
 #else /* LACKS_UNISTD_H */
 #if !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__)
 extern void*     sbrk(ptrdiff_t);