diff --git a/src/mzscheme/src/rational.c b/src/mzscheme/src/rational.c
index ef87c6d424..9fc0fe4db6 100644
--- a/src/mzscheme/src/rational.c
+++ b/src/mzscheme/src/rational.c
@@ -202,7 +202,7 @@ static int rational_lt(const Scheme_Object *a, const Scheme_Object *b, int or_eq
 
   /* Avoid multiplication in simple cases: */
   if (scheme_bin_lt_eq(ra->num, rb->num)
-      && scheme_bin_gt_eq(ra->num, rb->num)) {
+      && scheme_bin_gt_eq(ra->denom, rb->denom)) {
     if (!or_eq) {
       if (scheme_rational_eq(a, b))
         return 0;
diff --git a/src/mzscheme/src/schemef.h b/src/mzscheme/src/schemef.h
index 4a5199c698..585899b05d 100644
--- a/src/mzscheme/src/schemef.h
+++ b/src/mzscheme/src/schemef.h
@@ -930,7 +930,7 @@ MZ_EXTERN Scheme_Object *scheme_make_struct_exptime(Scheme_Object **names, int c
 						    Scheme_Object *super_exptime,
 						    int flags);
 
-MZ_EXTERN int scheme_is_struct_instance(Scheme_Object *type, Scheme_Object *v);
+XFORM_NONGCING MZ_EXTERN int scheme_is_struct_instance(Scheme_Object *type, Scheme_Object *v);
 MZ_EXTERN Scheme_Object *scheme_struct_ref(Scheme_Object *s, int pos);
 MZ_EXTERN void scheme_struct_set(Scheme_Object *s, int pos, Scheme_Object *v);