diff --git a/racket/src/README b/racket/src/README
index 7b3d953b0e..d7920f0e77 100644
--- a/racket/src/README
+++ b/racket/src/README
@@ -27,9 +27,9 @@ To compile with Microsoft Visual C, read the instructions in
 
 To compile with MinGW tools, follow the Unix instructions below; do not
 use `--enable-shared', because DLLs will be generated automatically.
-The result is a Windows-style build, but without MzCOM. If you are using
-a variant of MinGW without "libdelayimp.a", get the implementation of
-"delayimp.c" from MinGW-w64 and compile it to "libdelayimp.a".
+The result is a Windows-style build. If you are using a variant of
+MinGW without "libdelayimp.a", get the implementation of "delayimp.c"
+from MinGW-w64 and compile it to "libdelayimp.a".
 
 To compile with Cygwin tools, follow the Unix instructions below.  The
 result is a Unix-style build, not a Windows-style build (e.g.,
diff --git a/racket/src/mzcom/com_glue.c b/racket/src/mzcom/com_glue.c
index 48a9f0e0ac..9c8fcf0866 100644
--- a/racket/src/mzcom/com_glue.c
+++ b/racket/src/mzcom/com_glue.c
@@ -470,8 +470,9 @@ static STDMETHODIMP Advise(IConnectionPoint *com_obj, IUnknown *obj, DWORD *cook
 
   // We need to return (to the app) some value that will clue our Unadvise() function
   // below how to locate this app IMzObjEvents. The simpliest thing is to just use the
-  // app's IMzObjEvents pointer as that returned value
-  *cookie = (DWORD)iExample->evts;
+  // app's IMzObjEvents pointer as that returned value. We may lose some bits here,
+  // but that's ok:
+  *cookie = (DWORD)(intptr_t)iExample->evts;
 
   return(hr);
 }
@@ -496,10 +497,10 @@ static STDMETHODIMP Unadvise(IConnectionPoint *com_obj, DWORD cookie)
   // IMzObjEvents right now.
   //		
   // Let's just make sure the cookie he passed is really the pointer we expect
-  if (cookie && (IMzObjEvents *)cookie == iExample->evts)
+  if (cookie && cookie == (DWORD)(intptr_t)iExample->evts)
     {
       // Release the app's IMzObjEvents
-      ((IMzObjEvents *)cookie)->lpVtbl->Release((IMzObjEvents *)cookie);
+      iExample->evts->lpVtbl->Release(iExample->evts);
 
       // We no longer have the app's IMzObjEvents, so clear the IMzObj
       // feedback member
@@ -672,7 +673,7 @@ HRESULT com_register()
   // Initialize my IClassFactory with the pointer to its vtable
   MyIClassFactoryObj.lpVtbl = (IClassFactoryVtbl *)&IClassFactory_Vtbl;
 
-  return CoRegisterClassObject(&CLSID_IMzObj, &MyIClassFactoryObj,
+  return CoRegisterClassObject(&CLSID_IMzObj, (IUnknown*)&MyIClassFactoryObj,
                                CLSCTX_LOCAL_SERVER, REGCLS_SINGLEUSE, &reg_cookie);
 }
 
diff --git a/racket/src/mzcom/mzcom.cxx b/racket/src/mzcom/mzcom.cxx
index 263dd64f18..d87a5db74f 100644
--- a/racket/src/mzcom/mzcom.cxx
+++ b/racket/src/mzcom/mzcom.cxx
@@ -65,12 +65,12 @@ static bool StartMonitor() { return TRUE; }
 
 #endif
 
-static int set_reg_string(HKEY sub, char *name, char *s)
+static int set_reg_string(HKEY sub, const char *name, const char *s)
 {
   return RegSetValueExA(sub, name, 0, REG_SZ, (const BYTE *)s, strlen(s));
 }
 
-static int set_reg_sub_string(HKEY sub, char *name, char *s)
+static int set_reg_sub_string(HKEY sub, const char *name, const char *s)
 {
   HKEY sub2;
   int nRet;
@@ -86,10 +86,10 @@ static int set_reg_sub_string(HKEY sub, char *name, char *s)
 
 LPCTSTR FindOneOf(LPCTSTR p1, LPCTSTR p2)
 {
-  while (p1 != NULL && *p1 != NULL)
+  while (p1 != NULL && *p1 != 0)
     {
       LPCTSTR p = p2;
-      while (p != NULL && *p != NULL)
+      while (p != NULL && *p != 0)
         {
           if (*p1 == *p)
             return CharNext(p1);
diff --git a/racket/src/mzcom/mzobj.cxx b/racket/src/mzcom/mzobj.cxx
index e5df4c4487..698988656f 100644
--- a/racket/src/mzcom/mzobj.cxx
+++ b/racket/src/mzcom/mzobj.cxx
@@ -35,7 +35,7 @@ END_XFORM_SKIP;
 START_XFORM_SKIP;
 #endif
 
-static void ErrorBox(char *s) {
+static void ErrorBox(const char *s) {
   ::MessageBox(NULL,s,"MzCOM",MB_OK);
 }
 
@@ -112,12 +112,12 @@ static Scheme_Object *eval_string_or_get_exn_message(char *s) {
   return exn;
 }
 
-OLECHAR *wideStringFromSchemeObj(Scheme_Object *obj,char *fmt,int fmtlen) {
+OLECHAR *wideStringFromSchemeObj(Scheme_Object *obj,const char *fmt,int fmtlen) {
   char *s;
   OLECHAR *wideString;
   int len;
 
-  s = scheme_format_utf8(fmt,fmtlen,1,&obj,NULL);
+  s = scheme_format_utf8((char *)fmt,fmtlen,1,&obj,NULL);
   len = strlen(s);
   wideString = (OLECHAR *)scheme_malloc((len + 1) * sizeof(OLECHAR));
   MultiByteToWideChar(CP_ACP,(DWORD)0,s,len,wideString,len + 1);
@@ -133,7 +133,7 @@ void exitHandler(int) {
 
 void setupSchemeEnv(Scheme_Env *in_env)
 {
-  char *wrapper;
+  const char *wrapper;
   char exeBuff[260];
   HMODULE mod;
   static BOOL registered;
@@ -308,12 +308,10 @@ static int record_at_exit(Scheme_At_Exit_Callback_Proc p) XFORM_SKIP_PROC
   return 0;
 }
 
-static __declspec(thread) void *tls_space;
+#include "../racket/win_tls.inc"
 
 static unsigned WINAPI evalLoop(void *args) XFORM_SKIP_PROC {
-#ifndef _WIN64
-  scheme_register_tls_space(&tls_space, 0);
-#endif
+  register_win_tls();
   scheme_set_atexit(record_at_exit);
 
   return scheme_main_setup(1, do_evalLoop, 0, (char **)args);
@@ -563,6 +561,20 @@ HRESULT mzobj_eval(void *o, BSTR s, BSTR *r)
   return ((CMzObj *)o)->Eval(s, r);
 }
 
+#ifdef __MINGW32__
+
+void * operator new(size_t n)
+{
+  return malloc(n);
+}
+
+void operator delete(void * p)
+{
+  free(p);
+}
+
+#endif
+
 #ifdef MZ_PRECISE_GC
 END_XFORM_SKIP;
 #endif
diff --git a/racket/src/mzcom/prebuilt/MzCOM.tlb b/racket/src/mzcom/prebuilt/MzCOM.tlb
new file mode 100644
index 0000000000..25ee5c77b5
Binary files /dev/null and b/racket/src/mzcom/prebuilt/MzCOM.tlb differ
diff --git a/racket/src/mzcom/prebuilt/README.txt b/racket/src/mzcom/prebuilt/README.txt
new file mode 100644
index 0000000000..46996bf6bc
--- /dev/null
+++ b/racket/src/mzcom/prebuilt/README.txt
@@ -0,0 +1,3 @@
+Scine MinGW doesn't currently include `widl`, since installing it with
+Wine is a pain, and since the output is not platform-specific, we
+include "MzCOM.tlb" as pre-built from "mzcom.idl".
diff --git a/racket/src/racket/Makefile.in b/racket/src/racket/Makefile.in
index d5c7edcca6..7c27d9b68a 100644
--- a/racket/src/racket/Makefile.in
+++ b/racket/src/racket/Makefile.in
@@ -89,13 +89,15 @@ cgc:
 	$(MAKE) common
 	$(MAKE) dynlib
 	$(MAKE) mzlibrary
-	$(MAKE) racket@CGC@ 
+	$(MAKE) racket@CGC@
+	$(MAKE) mzcom@CGC@
 
 3m:
 	$(MAKE) @CGC_IF_NEEDED_FOR_MMM@
 	cd gc2; $(MAKE) all
 	cd dynsrc; $(MAKE) dynlib3m
 	cd gc2; $(MAKE) ../racket@MMM@
+	cd gc2; $(MAKE) ../mzcom@MMM@
 
 both:
 	$(MAKE) cgc
@@ -173,6 +175,9 @@ sproc.@LTO@: @GCDIR@/sproc.@LTO@
 racket@CGC@@NOT_OSX@@NOT_MINGW@: libracket.@LIBSFX@ libmzgc.@LIBSFX@ main.@LTO@ $(SPECIALIZINGOBJECTS)
 	@MZLINKER@ -o racket@CGC@ main.@LTO@ $(SPECIALIZINGOBJECTS) libracket.@LIBSFX@ libmzgc.@LIBSFX@ @LDFLAGS@ @LIBS@
 
+mzcom@CGC@@NOT_MINGW@:
+	$(NOOP)
+
 # Mac OS ----------------------------------------
 
 MZFW = Racket.framework/Versions/$(FWVERSION)/Racket
@@ -209,15 +214,23 @@ libmzgc.dll.a: lib/libmzgcxxxxxxx.dll
 rres.o : $(srcdir)/../worksp/racket/racket.rc
 	@WINDRES@ -i $(srcdir)/../worksp/racket/racket.rc -o rres.o
 
-racket@CGC@@MINGW@: libracket.dll.a libmzgc.dll.a main.@LTO@ $(SPECIALIZINGOBJECTS) rres.o
-	@MZLINKER@ -o racket@CGC@ main.@LTO@ rres.o $(SPECIALIZINGOBJECTS) libracket.dll.a libmzgc.dll.a @LDFLAGS@ @LIBS@ -ldelayimp -static-libgcc
+MW_RACKET_LIBS = libracket.dll.a libmzgc.dll.a @LDFLAGS@ @LIBS@ -ldelayimp -static-libgcc
 
-mingw-other@MINGW@: mzsj86g.o rres.o
+racket@CGC@@MINGW@: libracket.dll.a libmzgc.dll.a main.@LTO@ $(SPECIALIZINGOBJECTS) rres.o
+	@MZLINKER@ -o racket@CGC@ main.@LTO@ rres.o $(SPECIALIZINGOBJECTS) $(MW_RACKET_LIBS)
+
+mingw-other@MINGW@: mzsj86g.o rres.o comres.o com_glue.@LTO@
 	$(NOOP)
 
 mingw-other@NOT_MINGW@:
 	$(NOOP)
 
+mzcom@CGC@@MINGW@: libracket.dll.a libmzgc.dll.a mzcom.@LTO@ mzobj.@LTO@ com_glue.@LTO@ $(SPECIALIZINGOBJECTS) comres.o
+	@MZLINKER@ -o mzcom@CGC@ mzcom.@LTO@ mzobj.@LTO@ com_glue.@LTO@ comres.o $(SPECIALIZINGOBJECTS) -lole32 -loleaut32 -luuid $(MW_RACKET_LIBS)
+
+comres.o : $(srcdir)/../worksp/mzcom/mzcom.rc $(srcdir)/../mzcom/prebuilt/MzCOM.tlb
+	@WINDRES@ -I $(srcdir)/../mzcom -I $(srcdir)/../mzcom/prebuilt -i $(srcdir)/../worksp/mzcom/mzcom.rc -o comres.o
+
 # OSKit ----------------------------------------
 
 racket.multiboot : libracket.@LIBSFX@ libmzgc.@LIBSFX@ main.@LTO@
@@ -238,7 +251,7 @@ DEF_C_DIRS = $(DEF_COLLECTS_DIR) $(DEF_CONFIG_DIR)
 
 MAIN_HEADER_DEPS = $(srcdir)/include/scheme.h $(srcdir)/include/schthread.h $(srcdir)/sconfig.h \
                    $(srcdir)/src/stypes.h $(srcdir)/cmdline.inc $(srcdir)/parse_cmdl.inc \
-	           $(srcdir)/oskglue.inc
+	           $(srcdir)/oskglue.inc $(srcdir)/delayed.inc $(srcdir)/parse_cmdl.inc
 
 main.@LTO@: $(srcdir)/main.c $(MAIN_HEADER_DEPS)
 	$(CC) -I$(builddir) -I$(srcdir)/include $(CFLAGS) $(CPPFLAGS) @OPTIONS@ @MZOPTIONS@ $(DEF_C_DIRS) -c $(srcdir)/main.c -o main.@LTO@
@@ -257,6 +270,17 @@ mzstart.exe: $(srcdir)/dynsrc/start.c
 
 starter: mzstart.exe
 
+MZCOM_DEPS = $(MAIN_HEADER_DEPS) $(srcdir)/../mzcom/com_glue.h $(srcdir)/../mzcom/resource.h
+
+mzcom.@LTO@: $(srcdir)/../mzcom/mzcom.cxx $(MZCOM_DEPS)
+	$(CC) -fno-exceptions -I$(builddir) -I$(srcdir)/include $(CFLAGS) $(CPPFLAGS) @OPTIONS@ @MZOPTIONS@ $(DEF_C_DIRS) -c $(srcdir)/../mzcom/mzcom.cxx -o mzcom.@LTO@
+
+mzobj.@LTO@: $(srcdir)/../mzcom/mzobj.cxx $(MZCOM_DEPS)
+	$(CC) -fno-exceptions -I$(builddir) -I$(srcdir)/include $(CFLAGS) $(CPPFLAGS) @OPTIONS@ @MZOPTIONS@ -c $(srcdir)/../mzcom/mzobj.cxx -o mzobj.@LTO@
+
+com_glue.@LTO@: $(srcdir)/../mzcom/com_glue.c $(MZCOM_DEPS)
+	$(CC) -I$(builddir) -I$(srcdir)/include $(CFLAGS) $(CPPFLAGS) @OPTIONS@ @MZOPTIONS@ -c $(srcdir)/../mzcom/com_glue.c -o com_glue.@LTO@
+
 exn:
 	$(MAKE) $(srcdir)/src/schexn.h
 	$(MAKE) $(collectsdir)/racket/private/kernstruct.rkt
@@ -403,14 +427,18 @@ mingw-install:
 	cd ..; cp racket/mrstarter@EXE_SUFFIX@ "$(DESTDIR)$(libpltdir)/MrStart@EXE_SUFFIX@"
 	cd ..; $(STRIP_DEBUG) "$(DESTDIR)$(libpltdir)/MzStart@EXE_SUFFIX@"
 	cd ..; $(STRIP_DEBUG) "$(DESTDIR)$(libpltdir)/MrStart@EXE_SUFFIX@"
+	cp "$(srcdir)/../mzcom/prebuilt/MzCOM.tlb" MzCOM.tlb
+	cd ..; cp racket/MzCOM.tlb "$(DESTDIR)$(libpltdir)/MzCOM.tlb"
 
 mingw-install-cgc:
 	cd ..; $(ICP) racket/lib/libmzgcxxxxxxx.dll "$(DESTDIR)$(libdir)/libmzgcxxxxxxx.dll"
 	cd ..; $(ICP) racket/lib/libracketxxxxxxx.dll "$(DESTDIR)$(libdir)/libracketxxxxxxx.dll"
 	cd ..; $(ICP) racket/racket@CGC@ "$(DESTDIR)@MZINSTALLBINDIR@/Racket@CGC_INSTALLED@@EXE_SUFFIX@"
+	cd ..; $(ICP) racket/mzcom@CGC@ "$(DESTDIR)$(libdir)/MzCOM@CGC_INSTALLED@@EXE_SUFFIX@"
 	cd ..; $(STRIP_DEBUG) "$(DESTDIR)$(libdir)/libmzgcxxxxxxx.dll"
 	cd ..; $(STRIP_DEBUG) "$(DESTDIR)$(libdir)/libracketxxxxxxx.dll"
 	cd ..; $(STRIP_DEBUG) "$(DESTDIR)@MZINSTALLBINDIR@/Racket@CGC_INSTALLED@@EXE_SUFFIX@"
+	cd ..; $(STRIP_DEBUG) "$(DESTDIR)$(libdir)/MzCOM@CGC_INSTALLED@@EXE_SUFFIX@"
 	@RUN_RACKET_CGC@ -cu "$(srcdir)/collects-path.rkt" @DIRCVTPRE@"$(DESTDIR)@MZINSTALLBINDIR@/Racket@CGC_INSTALLED@@EXE_SUFFIX@"@DIRCVTPOST@ $(DESTDIR)@COLLECTS_PATH@ $(DESTDIR)@CONFIG_PATH@
 
 mingw-install-cgc-final:
@@ -418,9 +446,11 @@ mingw-install-cgc-final:
 
 mingw-install-3m:
 	cd ..; $(ICP) racket/racket@MMM@ "$(DESTDIR)@MZINSTALLBINDIR@/Racket@MMM_INSTALLED@@EXE_SUFFIX@"
+	cd ..; $(ICP) racket/mzcom@MMM@ "$(DESTDIR)$(libdir)/MzCOM@MMM_INSTALLED@@EXE_SUFFIX@"
 	cd ..; $(ICP) racket/lib/libracket3mxxxxxxx.dll "$(DESTDIR)$(libdir)/libracket3mxxxxxxx.dll"
-	cd ..; $(STRIP_DEBUG) "$(DESTDIR)@MZINSTALLBINDIR@/Racket@MMM_INSTALLED@@EXE_SUFFIX@"
 	cd ..; $(STRIP_DEBUG) "$(DESTDIR)$(libdir)/libracket3mxxxxxxx.dll"
+	cd ..; $(STRIP_DEBUG) "$(DESTDIR)@MZINSTALLBINDIR@/Racket@MMM_INSTALLED@@EXE_SUFFIX@"
+	cd ..; $(STRIP_DEBUG) "$(DESTDIR)$(libdir)/MzCOM@MMM_INSTALLED@@EXE_SUFFIX@"
 	@RUN_RACKET_MMM@ -cu "$(srcdir)/collects-path.rkt" @DIRCVTPRE@"$(DESTDIR)@MZINSTALLBINDIR@/Racket@MMM_INSTALLED@@EXE_SUFFIX@"@DIRCVTPOST@ $(DESTDIR)@COLLECTS_PATH@ $(DESTDIR)@CONFIG_PATH@
 
 mingw-install-3m-final:
diff --git a/racket/src/racket/delayed.inc b/racket/src/racket/delayed.inc
index 96a5b1ffe1..551e4d4f93 100644
--- a/racket/src/racket/delayed.inc
+++ b/racket/src/racket/delayed.inc
@@ -21,10 +21,10 @@ static int _dlldir_offset = 14; /* Skip permanent tag */
 START_XFORM_SKIP;
 # endif
 
-static void load_delayed_dll(HINSTANCE me, char *lib) 
+static void load_delayed_dll(HINSTANCE me, const char *lib) 
 {
   /* Don't use the C library here! */
-  wchar_t *dlldir = _dlldir + _dlldir_offset;
+  const wchar_t *dlldir = _dlldir + _dlldir_offset;
 
   if (dlldir[0] != '<') {
     if ((dlldir[0] == '\\')
diff --git a/racket/src/racket/gc2/Makefile.in b/racket/src/racket/gc2/Makefile.in
index e2051fd08a..2e33b27767 100644
--- a/racket/src/racket/gc2/Makefile.in
+++ b/racket/src/racket/gc2/Makefile.in
@@ -313,6 +313,9 @@ $(XSRCDIR)/foreign.c: $(XFORMDEP)
 $(XSRCDIR)/main.c: $(XFORMDEP)
 	$(XFORM_NOPRECOMP) $(XSRCDIR)/main.c $(DEF_C_DIRS) $(srcdir)/../main.c
 
+$(XSRCDIR)/mzobj.cxx: $(XFORMDEP)
+	$(XFORM_NOPRECOMP) $(XSRCDIR)/mzobj.cxx $(DEF_C_DIRS) $(srcdir)/../../mzcom/mzobj.cxx
+
 salloc.@LTO@: $(XSRCDIR)/salloc.c
 	$(CC) $(ALL_CFLAGS) -c $(XSRCDIR)/salloc.c -o salloc.@LTO@
 bignum.@LTO@: $(XSRCDIR)/bignum.c
@@ -428,6 +431,11 @@ foreign.@LTO@: $(XSRCDIR)/foreign.c
 main.@LTO@: $(XSRCDIR)/main.c
 	$(CC) $(ALL_CFLAGS) -c $(XSRCDIR)/main.c -o main.@LTO@
 
+mzcom.@LTO@: $(srcdir)/../../mzcom/mzcom.cxx
+	$(CC) -DMZCOM_3M $(ALL_CFLAGS) -fno-exceptions -c $(srcdir)/../../mzcom/mzcom.cxx -o mzcom.@LTO@
+mzobj.@LTO@: $(XSRCDIR)/mzobj.cxx
+	$(CC) $(ALL_CFLAGS) -fno-exceptions -c $(XSRCDIR)/mzobj.cxx -o mzobj.@LTO@
+
 gc2.@LTO@: \
 		$(srcdir)/alloc_cache.c \
 		$(srcdir)/block_cache.c \
@@ -523,9 +531,16 @@ $(MZFWMMM): ../libracket3m.@LIBSFX@
 libracket3m.dll.a: ../lib/libracket3mxxxxxxx.dll
 	@DLLTOOL@ --def libracket3m.def -D libracket3mxxxxxxx.dll --output-delaylib libracket3m.dll.a
 
-../racket@MMM@@MINGW@: libracket3m.dll.a main.@LTO@ ../rres.o $(SPECIALIZINGOBJECTS)
-	cd ..; @MZLINKER@ -o racket@MMM@ gc2/main.@LTO@ rres.o $(SPECIALIZINGOBJECTS) gc2/libracket3m.dll.a @LDFLAGS@ @LIBS@ -ldelayimp -static-libgcc
+MW_RACKET_LIBS = gc2/libracket3m.dll.a @LDFLAGS@ @LIBS@ -ldelayimp -static-libgcc
 
+../racket@MMM@@MINGW@: libracket3m.dll.a main.@LTO@ ../rres.o $(SPECIALIZINGOBJECTS)
+	cd ..; @MZLINKER@ -o racket@MMM@ gc2/main.@LTO@ rres.o $(SPECIALIZINGOBJECTS) $(MW_RACKET_LIBS)
+
+../mzcom@MMM@@NOT_MINGW@:
+	$(NOOP)
+
+../mzcom@MMM@@MINGW@: libracket3m.dll.a mzcom.@LTO@ mzobj.@LTO@ ../com_glue.@LTO@ $(SPECIALIZINGOBJECTS) ../comres.o
+	cd ..; @MZLINKER@ -o mzcom@MMM@ gc2/mzcom.@LTO@ gc2/mzobj.@LTO@ com_glue.@LTO@ comres.o $(SPECIALIZINGOBJECTS) -lole32 -loleaut32 -luuid $(MW_RACKET_LIBS)
 
 clean:
 	/bin/rm -f ../racket@MMM@ *.@LTO@ $(XSRCDIR)/*
diff --git a/racket/src/racket/main.c b/racket/src/racket/main.c
index 47dcbf98c2..690c5d2068 100644
--- a/racket/src/racket/main.c
+++ b/racket/src/racket/main.c
@@ -292,13 +292,8 @@ START_XFORM_SKIP;
 # include "parse_cmdl.inc"
 #endif
 
-#ifdef IMPLEMENT_THREAD_LOCAL_VIA_WIN_TLS
-extern intptr_t _tls_index;
-# ifdef __MINGW32__
-static __thread void *tls_space;
-# else
-static __declspec(thread) void *tls_space;
-# endif
+#ifdef DOS_FILE_SYSTEM
+# include "win_tls.inc"
 #endif
 
 #ifdef DOS_FILE_SYSTEM
@@ -314,25 +309,8 @@ void load_delayed()
   load_delayed_dll(NULL, "libracket" DLL_3M_SUFFIX "xxxxxxx.dll");
 # endif
   record_dll_path();
-# ifdef IMPLEMENT_THREAD_LOCAL_VIA_WIN_TLS
-#  ifdef __MINGW32__
-  {
-    /* gcc declares space for the thread-local variable in a way that
-       the OS can set up, but its doesn't actually map variables
-       through the OS-supplied mechanism. Just assume that the first
-       thread-local variable is ours. */
-    void **base;
-#  ifdef _WIN64
-    asm("mov %%gs:(0x58), %0;" :"=r"(base));
-#  else
-    asm("mov %%fs:(0x2C), %0;" :"=r"(base));
-#  endif
-    scheme_register_tls_space(*base, _tls_index);
-  }
-#  else
-  scheme_register_tls_space(&tls_space, _tls_index);
-#  endif
-# endif
+
+  register_win_tls();
 }
 #endif
 
diff --git a/racket/src/racket/src/mzrt.c b/racket/src/racket/src/mzrt.c
index c3a5cdc7bb..7cd89e26b6 100644
--- a/racket/src/racket/src/mzrt.c
+++ b/racket/src/racket/src/mzrt.c
@@ -328,7 +328,8 @@ int mz_proc_thread_detach(mz_proc_thread *thread) {
 
 void mz_proc_thread_exit(void *rc) {
 #ifdef WIN32
-  _endthreadex((unsigned)rc);
+  proc_thread_self->res = rc;
+  _endthreadex(0);
 #else
 #   ifndef MZ_PRECISE_GC
   pthread_exit(rc);
diff --git a/racket/src/racket/win_tls.inc b/racket/src/racket/win_tls.inc
new file mode 100644
index 0000000000..fdfc3376bb
--- /dev/null
+++ b/racket/src/racket/win_tls.inc
@@ -0,0 +1,33 @@
+#ifdef IMPLEMENT_THREAD_LOCAL_VIA_WIN_TLS
+extern intptr_t _tls_index;
+# ifdef __MINGW32__
+static __thread void *tls_space;
+# else
+static __declspec(thread) void *tls_space;
+# endif
+#endif
+
+# ifdef IMPLEMENT_THREAD_LOCAL_VIA_WIN_TLS
+static void register_win_tls()
+{
+#  ifdef __MINGW32__
+  {
+    /* gcc declares space for the thread-local variable in a way that
+       the OS can set up, but its doesn't actually map variables
+       through the OS-supplied mechanism. Just assume that the first
+       thread-local variable is ours. */
+    void **base;
+#  ifdef _WIN64
+    asm("mov %%gs:(0x58), %0;" :"=r"(base));
+#  else
+    asm("mov %%fs:(0x2C), %0;" :"=r"(base));
+#  endif
+    scheme_register_tls_space(*base, _tls_index);
+  }
+#  else
+  scheme_register_tls_space(&tls_space, _tls_index);
+#  endif
+}
+# else
+static void register_win_tls() {}
+# endif