diff --git a/gc.c b/gc.c
index e6c3d1940f..2c11b07d41 100644
--- a/gc.c
+++ b/gc.c
@@ -138,6 +138,10 @@
 #define rb_jmp_buf rb_jmpbuf_t
 #undef rb_data_object_wrap
 
+#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+
 static inline struct rbimpl_size_mul_overflow_tag
 size_add_overflow(size_t x, size_t y)
 {