diff --git a/dtool/src/dtoolbase/memoryHook.cxx b/dtool/src/dtoolbase/memoryHook.cxx
index 49354f1ae8..01cebd5268 100644
--- a/dtool/src/dtoolbase/memoryHook.cxx
+++ b/dtool/src/dtoolbase/memoryHook.cxx
@@ -29,6 +29,10 @@
 #include <sys/types.h>
 #include <sys/mman.h>
 
+#ifndef MAP_ANON
+#define MAP_ANON 0x1000
+#endif
+
 #endif  // WIN32
 
 
@@ -447,7 +451,7 @@ mmap_alloc(size_t size, bool allow_exec) {
   if (allow_exec) {
     prot |= PROT_EXEC;
   }
-  void *ptr = mmap(NULL, size, prot, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  void *ptr = mmap(NULL, size, prot, MAP_PRIVATE | MAP_ANON, -1, 0);
   if (ptr == (void *)-1) {
     perror("mmap");
     abort();