diff --git a/src/README b/src/README
index 9f254df51b..278dd29917 100644
--- a/src/README
+++ b/src/README
@@ -360,6 +360,13 @@ Configuration Options
 Athough `configure' flags control most options, some configrations
 options can be modified by setting flags in "racket/sconfig.h".
 
+Some CPP flags control default settings in "racket/sconfig.h":
+
+ * MZ_{USE_,NO_}JIT_SSE - {en,dis}ables use of SSE floating point
+
+ * MZ_USE_DETERMINSTIC_FUEL - disables use of itimer or pthread for
+   Racket thread scheduling.
+
 Modifying Racket
 ----------------
 
diff --git a/src/foreign/Makefile.in b/src/foreign/Makefile.in
index 7d50a079f7..3b6a3c0873 100644
--- a/src/foreign/Makefile.in
+++ b/src/foreign/Makefile.in
@@ -34,6 +34,7 @@ libffi/libffi@FOREIGN_CONVENIENCE@.la:
 	cd libffi; $(MAKE) libffi@FOREIGN_CONVENIENCE@.la
 
 foreign.@LTO@: $(srcdir)/foreign.c \
+           $(srcdir)/../racket/sconfig.h \
            $(srcdir)/../racket/include/scheme.h \
            $(srcdir)/../racket/include/schthread.h \
            $(srcdir)/../racket/src/schemef.h \
diff --git a/src/racket/sconfig.h b/src/racket/sconfig.h
index f5b923c5c5..8ed9860560 100644
--- a/src/racket/sconfig.h
+++ b/src/racket/sconfig.h
@@ -597,7 +597,9 @@
 # define NO_SLEEP
 # define WINDOWS_PROCESSES
 # define WINDOWS_FILE_HANDLES
-# define USE_WIN32_THREAD_TIMER
+# ifndef MZ_USE_DETERMINSTIC_FUEL
+#  define USE_WIN32_THREAD_TIMER
+# endif
 
 # define SIGSET_IS_SIGNAL
 # define SIGSET_NEEDS_REINSTALL
@@ -728,8 +730,10 @@
 # define SYSTEM_TYPE_NAME "macosx"
 #endif
 
-# undef USE_ITIMER
-# define USE_PTHREAD_THREAD_TIMER
+# ifndef MZ_USE_DETERMINSTIC_FUEL
+#  undef USE_ITIMER
+#  define USE_PTHREAD_THREAD_TIMER
+# endif
 
 # define USE_MAP_ANON
 
diff --git a/src/racket/src/jit.c b/src/racket/src/jit.c
index 78d8a87156..49d2863388 100644
--- a/src/racket/src/jit.c
+++ b/src/racket/src/jit.c
@@ -1058,6 +1058,23 @@ static int finish_branch(mz_jit_state *jitter, int target, Branch_Info *for_bran
 
 #ifdef USE_FLONUM_UNBOXING
 
+int scheme_generate_flonum_local_boxing(mz_jit_state *jitter, int pos, int offset, int target)
+{
+  GC_CAN_IGNORE jit_insn *ref;
+  __START_TINY_JUMPS__(1);
+  ref = jit_bnei_p(jit_forward(), target, NULL);
+  __END_TINY_JUMPS__(1);
+  CHECK_LIMIT();
+  jit_movi_l(JIT_R0, offset);
+  (void)jit_calli(sjc.box_flonum_from_stack_code);
+  mz_rs_stxi(pos, JIT_R0);
+  __START_TINY_JUMPS__(1);
+  mz_patch_branch(ref);
+  __END_TINY_JUMPS__(1);
+
+  return 1;
+}
+
 static int generate_flonum_local_boxing(mz_jit_state *jitter, int pos, int local_pos, int target)
 {
   int offset;
@@ -1069,18 +1086,8 @@ static int generate_flonum_local_boxing(mz_jit_state *jitter, int pos, int local
     jit_ldxi_d_fppush(fpr0, JIT_FP, offset);
     jitter->unbox_depth++;
   } else {
-    GC_CAN_IGNORE jit_insn *ref;
     mz_rs_sync();
-    __START_TINY_JUMPS__(1);
-    ref = jit_bnei_p(jit_forward(), target, NULL);
-    __END_TINY_JUMPS__(1);
-    CHECK_LIMIT();
-    jit_movi_l(JIT_R0, offset);
-    (void)jit_calli(sjc.box_flonum_from_stack_code);
-    mz_rs_stxi(pos, JIT_R0);
-    __START_TINY_JUMPS__(1);
-    mz_patch_branch(ref);
-    __END_TINY_JUMPS__(1);
+    scheme_generate_flonum_local_boxing(jitter, pos, offset, target);
   }
 
   return 1;
@@ -3292,7 +3299,7 @@ static int do_generate_closure(mz_jit_state *jitter, void *_data)
     GC_CAN_IGNORE jit_insn *zref;
     int f_offset;
 
-    /* In the case of an direct native call, the flonums can be
+    /* In the case of a direct native call, the flonums can be
        already unpacked, in which case JIT_SP is set up. Check whether
        JIT_SP is already different than the 0-flonums case. */
     f_offset = JIT_FRAME_FLONUM_OFFSET - (jitter->flostack_space * sizeof(double));
diff --git a/src/racket/src/jit.h b/src/racket/src/jit.h
index d53fde2882..929631ca67 100644
--- a/src/racket/src/jit.h
+++ b/src/racket/src/jit.h
@@ -417,6 +417,9 @@ void *scheme_jit_get_threadlocal_table();
 #  define _mz_tl_str_p(addr, tmp_reg, reg) jit_str_p(tmp_reg, reg)
 #  define _mz_tl_str_l(addr, tmp_reg, reg) jit_str_l(tmp_reg, reg)
 #  define _mz_tl_str_i(addr, tmp_reg, reg) jit_str_i(tmp_reg, reg)
+#  define mz_tl_addr_tmp_i(tmp_reg, addr) (jit_movr_l(JIT_R10, tmp_reg), mz_tl_addr(tmp_reg, addr))
+#  define mz_tl_addr_untmp_i(tmp_reg) jit_movr_l(tmp_reg, JIT_R10)
+#  define mz_tl_tmp_reg_i(tmp_reg) tmp_reg
 # else
 #  define THREAD_LOCAL_USES_JIT_V2
 #  ifdef THREAD_LOCAL_USES_JIT_V2
@@ -436,12 +439,15 @@ void *scheme_jit_get_threadlocal_table();
 #   define _mz_tl_str_l(addr, tmp_reg, reg) jit_str_l(tmp_reg, reg)
 #   define _mz_tl_str_i(addr, tmp_reg, reg) jit_str_i(tmp_reg, reg)
 #  endif
+#  define mz_tl_addr_tmp_i(tmp_reg, addr) mz_tl_addr_tmp(tmp_reg, addr)
+#  define mz_tl_addr_untmp_i(tmp_reg) mz_tl_addr_untmp(tmp_reg)
+#  define mz_tl_tmp_reg_i(tmp_reg) mz_tl_tmp_reg(tmp_reg)
 # endif
 
 /* A given tmp_reg doesn't have to be unused; it just has to be distinct from other arguments. */
 # define mz_tl_sti_p(addr, reg, tmp_reg) (mz_tl_addr_tmp(tmp_reg, addr), _mz_tl_str_p(addr, mz_tl_tmp_reg(tmp_reg), reg), mz_tl_addr_untmp(tmp_reg))
 # define mz_tl_sti_l(addr, reg, tmp_reg) (mz_tl_addr_tmp(tmp_reg, addr), _mz_tl_str_l(addr, mz_tl_tmp_reg(tmp_reg), reg), mz_tl_addr_untmp(tmp_reg))
-# define mz_tl_sti_i(addr, reg, tmp_reg) (mz_tl_addr_tmp(tmp_reg, addr), _mz_tl_str_i(addr, mz_tl_tmp_reg(tmp_reg), reg), mz_tl_addr_untmp(tmp_reg))
+# define mz_tl_sti_i(addr, reg, tmp_reg) (mz_tl_addr_tmp_i(tmp_reg, addr), _mz_tl_str_i(addr, mz_tl_tmp_reg_i(tmp_reg), reg), mz_tl_addr_untmp_i(tmp_reg))
 # define mz_tl_ldi_p(reg, addr) (mz_tl_addr(reg, addr), jit_ldr_p(reg, reg))
 # define mz_tl_ldi_l(reg, addr) (mz_tl_addr(reg, addr), jit_ldr_l(reg, reg))
 # define mz_tl_ldi_i(reg, addr) (mz_tl_addr(reg, addr), jit_ldr_i(reg, reg))
@@ -1264,6 +1270,7 @@ int scheme_generate_unboxed(Scheme_Object *obj, mz_jit_state *jitter, int inline
 
 #ifdef USE_FLONUM_UNBOXING
 int scheme_generate_flonum_local_unboxing(mz_jit_state *jitter, int push);
+int scheme_generate_flonum_local_boxing(mz_jit_state *jitter, int pos, int offset, int target);
 #endif
 int scheme_generate_unboxed(Scheme_Object *obj, mz_jit_state *jitter, int inlined_ok, int unbox_anyway);
 int scheme_generate_non_tail_mark_pos_prefix(mz_jit_state *jitter);
diff --git a/src/racket/src/jitarith.c b/src/racket/src/jitarith.c
index dc86d7a66b..19a2e93079 100644
--- a/src/racket/src/jitarith.c
+++ b/src/racket/src/jitarith.c
@@ -375,7 +375,7 @@ int scheme_generate_unboxing(mz_jit_state *jitter, int target)
   int fpr0;
 
   fpr0 = JIT_FPR_0(jitter->unbox_depth);
-  jit_ldxi_d_fppush(fpr0, target, &((Scheme_Double *)0x0)->double_val);  
+  jit_ldxi_d_fppush(fpr0, target, &((Scheme_Double *)0x0)->double_val);
   jitter->unbox_depth++;
 
   return 1;
diff --git a/src/racket/src/jitcall.c b/src/racket/src/jitcall.c
index 18d1405cf7..e4541149a4 100644
--- a/src/racket/src/jitcall.c
+++ b/src/racket/src/jitcall.c
@@ -1165,18 +1165,19 @@ static int generate_self_tail_call(Scheme_Object *rator, mz_jit_state *jitter, i
         GC_CAN_IGNORE jit_insn *iref;
         mz_pushr_p(JIT_R0);
         mz_ld_runstack_base_alt(JIT_R2);
-        jit_subi_p(JIT_R2, JIT_RUNSTACK_BASE_OR_ALT(JIT_R2), WORDS_TO_BYTES(num_rands + closure_size + args_already_in_place)); 
-        jit_ldxi_p(JIT_R0, JIT_R2, WORDS_TO_BYTES(i+closure_size));
+        jit_subi_p(JIT_R2, JIT_RUNSTACK_BASE_OR_ALT(JIT_R2), WORDS_TO_BYTES(num_rands + args_already_in_place)); 
+        jit_ldxi_p(JIT_R0, JIT_R2, WORDS_TO_BYTES(i));
         mz_rs_sync();
         __START_TINY_JUMPS__(1);
         iref = jit_bnei_p(jit_forward(), JIT_R0, NULL);
         __END_TINY_JUMPS__(1);
         {
-          mz_ld_fppush(JIT_FPR0, arg_tmp_offset);
+          int aoffset = JIT_FRAME_FLONUM_OFFSET - (arg_tmp_offset * sizeof(double));
+          jit_movi_l(JIT_R0, aoffset);
           (void)jit_calli(sjc.box_flonum_from_stack_code);
           mz_ld_runstack_base_alt(JIT_R2);
-          jit_subi_p(JIT_R2, JIT_RUNSTACK_BASE_OR_ALT(JIT_R2), WORDS_TO_BYTES(num_rands + closure_size + args_already_in_place)); 
-          jit_stxi_p(WORDS_TO_BYTES(i+closure_size), JIT_R2, JIT_R0);
+          jit_subi_p(JIT_R2, JIT_RUNSTACK_BASE_OR_ALT(JIT_R2), WORDS_TO_BYTES(num_rands + args_already_in_place)); 
+          jit_stxi_p(WORDS_TO_BYTES(i), JIT_R2, JIT_R0);
         }
         __START_TINY_JUMPS__(1);
         mz_patch_branch(iref);
@@ -1501,7 +1502,7 @@ static int generate_call_path_with_unboxes(mz_jit_state *jitter, int direct_flos
                                            GC_CAN_IGNORE jit_insn **_refdone,
                                            int num_rands, Scheme_Closure_Data *direct_data, Scheme_Object *rator)
 {
-  GC_CAN_IGNORE jit_insn *refdone, *refgo, *refcopy, *ref;
+  GC_CAN_IGNORE jit_insn *refdone, *refgo, *refcopy;
   int i, k, offset;
 
   refgo = jit_jmpi(jit_forward());
@@ -1547,16 +1548,7 @@ static int generate_call_path_with_unboxes(mz_jit_state *jitter, int direct_flos
       offset = jitter->flostack_offset - direct_flostack_offset + k;
       offset = JIT_FRAME_FLONUM_OFFSET - (offset * sizeof(double));
       jit_ldxi_p(JIT_R0, JIT_RUNSTACK, WORDS_TO_BYTES(i));
-      __START_TINY_JUMPS__(1);
-      ref = jit_bnei_p(jit_forward(), JIT_R0, NULL);
-      __END_TINY_JUMPS__(1);
-      CHECK_LIMIT();
-      jit_movi_l(JIT_R0, offset);
-      (void)jit_calli(sjc.box_flonum_from_stack_code);
-      jit_stxi_p(WORDS_TO_BYTES(i), JIT_RUNSTACK, JIT_R0);
-      __START_TINY_JUMPS__(1);
-      mz_patch_branch(ref);
-      __END_TINY_JUMPS__(1);
+      scheme_generate_flonum_local_boxing(jitter, i, offset, JIT_R0);
     }
   }
 
diff --git a/src/racket/uconfig.h b/src/racket/uconfig.h
index e7744c9b9a..bf334ae8a9 100644
--- a/src/racket/uconfig.h
+++ b/src/racket/uconfig.h
@@ -37,8 +37,10 @@
 
 #define USE_GETRUSAGE
 
-#if defined(MZ_USE_PLACES) || defined(USE_PTHREAD_INSTEAD_OF_ITIMER)
-# define USE_PTHREAD_THREAD_TIMER
-#else
-# define USE_ITIMER
+#ifndef MZ_USE_DETERMINSTIC_FUEL
+# if defined(MZ_USE_PLACES) || defined(USE_PTHREAD_INSTEAD_OF_ITIMER)
+#  define USE_PTHREAD_THREAD_TIMER
+# else
+#  define USE_ITIMER
+# endif
 #endif