diff --git a/src/foreign/foreign.c b/src/foreign/foreign.c
index ae237a110e..b0fd55bed5 100644
--- a/src/foreign/foreign.c
+++ b/src/foreign/foreign.c
@@ -84,6 +84,10 @@
 
 static void save_errno_values(int kind);
 
+/* This make hides pointerness from cdefstruct so that it
+   doesn't generate a mark/fixup action: */
+#define NON_GCBALE_PTR(t) t*
+
 /*****************************************************************************/
 /* Defining EnumProcessModules for openning `self' as an ffi-lib */
 
@@ -161,7 +165,7 @@ END_XFORM_SKIP;
 static Scheme_Type ffi_lib_tag;
 typedef struct ffi_lib_struct {
   Scheme_Object so;
-  void* handle;
+  NON_GCBALE_PTR(void) handle;
   Scheme_Object* name;
   Scheme_Hash_Table* objects;
 } ffi_lib_struct;
@@ -180,14 +184,12 @@ int ffi_lib_SIZE(void *p) {
 }
 int ffi_lib_MARK(void *p) {
   ffi_lib_struct *s = (ffi_lib_struct *)p;
-  gcMARK(s->handle);
   gcMARK(s->name);
   gcMARK(s->objects);
   return gcBYTES_TO_WORDS(sizeof(ffi_lib_struct));
 }
 int ffi_lib_FIXUP(void *p) {
   ffi_lib_struct *s = (ffi_lib_struct *)p;
-  gcFIXUP(s->handle);
   gcFIXUP(s->name);
   gcFIXUP(s->objects);
   return gcBYTES_TO_WORDS(sizeof(ffi_lib_struct));
@@ -271,9 +273,9 @@ static Scheme_Object *foreign_ffi_lib_name(int argc, Scheme_Object *argv[])
 static Scheme_Type ffi_obj_tag;
 typedef struct ffi_obj_struct {
   Scheme_Object so;
-  void* obj;
+  NON_GCBALE_PTR(void) obj;
   char* name;
-  ffi_lib_struct* lib;
+  NON_GCBALE_PTR(ffi_lib_struct) lib;
 } ffi_obj_struct;
 #define SCHEME_FFIOBJP(x) (SCHEME_TYPE(x)==ffi_obj_tag)
 #define MYNAME "ffi-obj?"
@@ -290,16 +292,12 @@ int ffi_obj_SIZE(void *p) {
 }
 int ffi_obj_MARK(void *p) {
   ffi_obj_struct *s = (ffi_obj_struct *)p;
-  gcMARK(s->obj);
   gcMARK(s->name);
-  gcMARK(s->lib);
   return gcBYTES_TO_WORDS(sizeof(ffi_obj_struct));
 }
 int ffi_obj_FIXUP(void *p) {
   ffi_obj_struct *s = (ffi_obj_struct *)p;
-  gcFIXUP(s->obj);
   gcFIXUP(s->name);
-  gcFIXUP(s->lib);
   return gcBYTES_TO_WORDS(sizeof(ffi_obj_struct));
 }
 END_XFORM_SKIP;
@@ -1049,13 +1047,13 @@ ffi_abi sym_to_abi(char *who, Scheme_Object *sym)
   if (SCHEME_FALSEP(sym) || SAME_OBJ(sym, default_sym))
     return FFI_DEFAULT_ABI;
   else if (SAME_OBJ(sym, sysv_sym)) {
-#if defined(WINDOWS_DYNAMIC_LOAD) && !defined(_WIN64)
+#ifdef WINDOWS_DYNAMIC_LOAD
     return FFI_SYSV;
 #else
     scheme_signal_error("%s: ABI not implemented: %V", who, sym);
 #endif
   } else if (SAME_OBJ(sym, stdcall_sym)) {
-#if defined(WINDOWS_DYNAMIC_LOAD) && !defined(_WIN64)
+#ifdef WINDOWS_DYNAMIC_LOAD
     return FFI_STDCALL;
 #else
     scheme_signal_error("%s: ABI not implemented: %V", who, sym);
@@ -1153,7 +1151,7 @@ static Scheme_Object *foreign_make_cstruct_type(int argc, Scheme_Object *argv[])
 static Scheme_Type ffi_callback_tag;
 typedef struct ffi_callback_struct {
   Scheme_Object so;
-  void* callback;
+  NON_GCBALE_PTR(void) callback;
   Scheme_Object* proc;
   Scheme_Object* itypes;
   Scheme_Object* otype;
@@ -1174,7 +1172,6 @@ int ffi_callback_SIZE(void *p) {
 }
 int ffi_callback_MARK(void *p) {
   ffi_callback_struct *s = (ffi_callback_struct *)p;
-  gcMARK(s->callback);
   gcMARK(s->proc);
   gcMARK(s->itypes);
   gcMARK(s->otype);
@@ -1183,7 +1180,6 @@ int ffi_callback_MARK(void *p) {
 }
 int ffi_callback_FIXUP(void *p) {
   ffi_callback_struct *s = (ffi_callback_struct *)p;
-  gcFIXUP(s->callback);
   gcFIXUP(s->proc);
   gcFIXUP(s->itypes);
   gcFIXUP(s->otype);
diff --git a/src/foreign/foreign.rktc b/src/foreign/foreign.rktc
index f517cfe844..de0a0609b0 100755
--- a/src/foreign/foreign.rktc
+++ b/src/foreign/foreign.rktc
@@ -87,6 +87,10 @@ exec racket "$0" > `echo "$0" | sed 's/rktc$/c/'` "$0"
 
 static void save_errno_values(int kind);
 
+/* This make hides pointerness from cdefstruct so that it
+   doesn't generate a mark/fixup action: */
+#define NON_GCBALE_PTR(t) t*
+
 /*****************************************************************************/
 /* Defining EnumProcessModules for openning `self' as an ffi-lib */
 
@@ -161,7 +165,7 @@ END_XFORM_SKIP;
 /* Library objects */
 
 @cdefstruct[ffi-lib
-  [handle  "void*"]
+  [handle  "NON_GCBALE_PTR(void)"]
   [name    "Scheme_Object*"]
   [objects "Scheme_Hash_Table*"]]
 
@@ -228,9 +232,9 @@ THREAD_LOCAL_DECL(static Scheme_Hash_Table *opened_libs);
 /* Pull pointers (mostly functions) out of ffi-lib objects */
 
 @cdefstruct[ffi-obj
-  [obj  "void*"]
+  [obj  "NON_GCBALE_PTR(void)"]
   [name "char*"]
-  [lib  "ffi_lib_struct*"]]
+  [lib  "NON_GCBALE_PTR(ffi_lib_struct)"]]
 
 /* (ffi-obj objname ffi-lib-or-libname) -> ffi-obj */
 @cdefine[ffi-obj 2]{
@@ -972,7 +976,7 @@ ffi_abi sym_to_abi(char *who, Scheme_Object *sym)
 /* Callback type */
 
 @cdefstruct[ffi-callback
-  [callback "void*"]
+  [callback "NON_GCBALE_PTR(void)"]
   [proc     "Scheme_Object*"]
   [itypes   "Scheme_Object*"]
   [otype    "Scheme_Object*"]
diff --git a/src/racket/src/salloc.c b/src/racket/src/salloc.c
index b8a3707ddd..497f7dbe14 100644
--- a/src/racket/src/salloc.c
+++ b/src/racket/src/salloc.c
@@ -1222,10 +1222,11 @@ void scheme_reset_finalizations(void)
   current_lifetime++;
 }
 
-static void do_next_finalization(void *o, void *data)
+static void do_next_finalization(void *o, void *_data)
 {
-  Finalizations *fns = *(Finalizations **)data;
+  Finalizations *fns = *(Finalizations **)_data;
   Finalization *fn;
+  GC_CAN_IGNORE void *data;
 
   if (fns->lifetime != current_lifetime)
     return;
@@ -1234,7 +1235,7 @@ static void do_next_finalization(void *o, void *data)
     if (fns->scheme_first->next || fns->ext_f || fns->prim_first) {
       /* Re-install low-level finalizer and run a scheme finalizer */
       GC_register_eager_finalizer(o, fns->scheme_first->next ? 1 : 2, 
-				  do_next_finalization, data, NULL, NULL);
+				  do_next_finalization, _data, NULL, NULL);
     }
 
     fn = fns->scheme_first;
@@ -1244,15 +1245,26 @@ static void do_next_finalization(void *o, void *data)
     else
       fn->next->prev = NULL;
 
-    fn->f(o, fn->data);
+    /* Clear out the `data' pointer, in case it refers to
+       memory that is free()ed, in which case the GC might
+       later take over the same page of memory. */
+    data = fn->data;
+    fn->data = NULL;
+
+    fn->f(o, data);
     return;
   }
 
-  if (fns->ext_f)
-    fns->ext_f(o, fns->ext_data);
+  if (fns->ext_f) {
+    data = fns->ext_data;
+    fns->ext_data = NULL;
+    fns->ext_f(o, data);
+  }
 
   for (fn = fns->prim_first; fn; fn = fn->next) {
-    fn->f(o, fn->data);
+    data = fn->data;
+    fn->data = NULL;
+    fn->f(o, data);
   }
 }