diff --git a/src/mzscheme/sgc/sgc.c b/src/mzscheme/sgc/sgc.c
index 548c60dd58..d3cfaedb47 100644
--- a/src/mzscheme/sgc/sgc.c
+++ b/src/mzscheme/sgc/sgc.c
@@ -776,8 +776,6 @@ static long mem_traced;
 static long num_chunks;
 static long num_blocks;
 
-typedef void (*GC_collect_start_callback_Proc)(void);
-typedef void (*GC_collect_end_callback_Proc)(void);
 GC_collect_start_callback_Proc GC_collect_start_callback;
 GC_collect_end_callback_Proc GC_collect_end_callback;
 void (*GC_custom_finalize)(void);
@@ -795,6 +793,7 @@ GC_collect_end_callback_Proc GC_set_collect_end_callback(GC_collect_end_callback
   return old;
 }
 
+
 static long roots_count;
 static long roots_size;
 static unsigned long *roots;
diff --git a/src/mzscheme/sgc/sgc.h b/src/mzscheme/sgc/sgc.h
index 6568beb2a8..ec54f37803 100644
--- a/src/mzscheme/sgc/sgc.h
+++ b/src/mzscheme/sgc/sgc.h
@@ -36,6 +36,11 @@ void *GC_malloc_stubborn(size_t size_in_bytes);
 void *GC_malloc_uncollectable(size_t size_in_bytes);
 void *GC_malloc_atomic_uncollectable(size_t size_in_bytes);
 
+typedef void (*GC_collect_start_callback_Proc)(void);
+typedef void (*GC_collect_end_callback_Proc)(void);
+GC_collect_start_callback_Proc GC_set_collect_start_callback(GC_collect_start_callback_Proc);
+GC_collect_end_callback_Proc GC_set_collect_end_callback(GC_collect_end_callback_Proc);
+
 void GC_free(void *); /* ... but only if it's turned on in sgc.c. */
 
 struct GC_Set;
diff --git a/src/mzscheme/src/thread.c b/src/mzscheme/src/thread.c
index acef8eda8f..39ca02d150 100644
--- a/src/mzscheme/src/thread.c
+++ b/src/mzscheme/src/thread.c
@@ -2147,7 +2147,7 @@ static Scheme_Thread *make_thread(Scheme_Config *config,
     scheme_fuel_counter_ptr = &scheme_fuel_counter;
 #endif
     
-#if defined(MZ_PRECISE_GC) || defined(USE_SENORA_GC)
+#if defined(MZ_PRECISE_GC)
     GC_set_get_thread_stack_base(scheme_get_current_thread_stack_start);
 #endif
     process->stack_start = stack_base;