diff --git a/src/mzscheme/gc/include/private/gc_priv.h b/src/mzscheme/gc/include/private/gc_priv.h
index ff91fb71e5..503728f9ad 100644
--- a/src/mzscheme/gc/include/private/gc_priv.h
+++ b/src/mzscheme/gc/include/private/gc_priv.h
@@ -414,7 +414,7 @@ extern GC_warn_proc GC_current_warn_proc;
 	  || defined (HAS_PPC_THREAD_STATE64___R0) \
 	  || defined (HAS_X86_THREAD_STATE32___EAX) \
 	  || defined (HAS_X86_THREAD_STATE64___RAX) \
-          || defined (__DARWIN_UNIX03)
+          || __DARWIN_UNIX03
 #         define THREAD_FLD(x) __ ## x
 #       else
 #         define THREAD_FLD(x) x
diff --git a/src/mzscheme/gc2/vm_osx.c b/src/mzscheme/gc2/vm_osx.c
index 4cf8233177..d569bf00e0 100644
--- a/src/mzscheme/gc2/vm_osx.c
+++ b/src/mzscheme/gc2/vm_osx.c
@@ -35,6 +35,12 @@ static int designate_modified(void *p);
 int designate_modified(void *p);
 #endif
 
+#if __DARWIN_UNIX03
+# define THREAD_FLD(x) __ ## x
+#else
+# define THREAD_FLD(x) x
+#endif
+
 #if defined(MZ_USE_PLACES) && defined (MZ_PRECISE_GC)
 typedef struct OSXThreadData {
   struct OSXThreadData *next;
@@ -283,7 +289,7 @@ kern_return_t GC_catch_exception_raise(mach_port_t port,
     mach_msg_type_number_t exc_state_count = x86_EXCEPTION_STATE64_COUNT;
     (void)thread_get_state(thread_port, x86_EXCEPTION_STATE64, (natural_t*)&exc_state,
                            &exc_state_count);
-    p = (void *)exc_state.__faultvaddr;
+    p = (void *)exc_state. THREAD_FLD(faultvaddr);
 #endif
 
 #if defined(MZ_USE_PLACES) && defined (MZ_PRECISE_GC)