diff --git a/src/mzscheme/gc2/newgc.c b/src/mzscheme/gc2/newgc.c
index 853f295e1c..95301fbbac 100644
--- a/src/mzscheme/gc2/newgc.c
+++ b/src/mzscheme/gc2/newgc.c
@@ -943,7 +943,7 @@ static void *get_backtrace(struct mpage *page, void *ptr)
   unsigned long delta;
 
   if (page->big_page)
-    ptr = PTR(page->addr + PREFIX_SIZE + WORD_SIZE);
+    ptr = PTR((char *)page->addr + PREFIX_SIZE + WORD_SIZE);
 
   delta = PPTR(ptr) - PPTR(page->addr);
   return page->backtrace[delta - 1];
diff --git a/src/mzscheme/src/salloc.c b/src/mzscheme/src/salloc.c
index 1f17ee6399..07691b4b63 100644
--- a/src/mzscheme/src/salloc.c
+++ b/src/mzscheme/src/salloc.c
@@ -1462,7 +1462,7 @@ static void cons_onto_list(void *p)
 # ifdef MZ_PRECISE_GC
 START_XFORM_SKIP;
 #  ifdef DOS_FILE_SYSTEM
-extern void gc_fprintf(int ignored, const char *c, ...);
+extern void gc_fprintf(FILE *ignored, const char *c, ...);
 #   define object_console_printf gc_fprintf
 #  endif
 # endif
@@ -2039,7 +2039,7 @@ Scheme_Object *scheme_dump_gc_stats(int c, Scheme_Object *p[])
         var_stack = (void **)t->jmpup_buf.gc_var_stack;
         delta = (long)t->jmpup_buf.stack_copy - (long)t->jmpup_buf.stack_from;
         /* FIXME: stack direction */
-        limit = (void *)t->jmpup_buf.stack_copy + t->jmpup_buf.stack_size;
+        limit = (char *)t->jmpup_buf.stack_copy + t->jmpup_buf.stack_size;
       }
       GC_dump_variable_stack(var_stack, delta, limit, NULL,
                              scheme_get_type_name,
diff --git a/src/worksp/gc2/make.ss b/src/worksp/gc2/make.ss
index f7635ae83d..6d271ce1bb 100644
--- a/src/worksp/gc2/make.ss
+++ b/src/worksp/gc2/make.ss
@@ -11,6 +11,7 @@
   (system s))
 
 (define accounting-gc? #t)
+(define backtrace-gc? #f)
 (define opt-flags "/O2 /Oy-")
 (define re:only #f)
 
@@ -169,6 +170,9 @@
 	(string-append "/D LIBMZ_EXPORTS "
 		       (if accounting-gc?
 			   "/D NEWGC_BTC_ACCOUNT "
+			   "")
+		       (if backtrace-gc?
+			   "/D MZ_GC_BACKTRACE "
 			   ""))
 	"mz.pch"
 	#f))
@@ -214,6 +218,9 @@
 	    (if accounting-gc?
 		"/D NEWGC_BTC_ACCOUNT "
 		"/D USE_COMPACT_3M_GC ")
+	    (if backtrace-gc?
+		"/D MZ_GC_BACKTRACE "
+		"")
 	    mz-inc))
 (c-compile "../../mzscheme/src/mzsj86.c" "xsrc/mzsj86.obj" '() mz-inc)
 
@@ -323,7 +330,10 @@
 	 wx-inc
 	 (and use-precomp? "xsrc/wxprecomp.h")
 	 "-DGC2_JUST_MACROS /FI../../../mzscheme/gc2/gc2.h"
-	 "-DGC2_AS_IMPORT"
+	 (string-append "-DGC2_AS_IMPORT"
+			(if backtrace-gc?
+			    " /D MZ_GC_BACKTRACE"
+			    ""))
 	 "wx.pch"
 	 indirect?)))