diff --git a/gc.c b/gc.c
index d8cd0074..5b7ac4c6 100644
--- a/gc.c
+++ b/gc.c
@@ -1103,6 +1103,22 @@ void gc_collector_trace()
   }
 }
 
+static void gc_collector_mark_gray(object parent, object obj)
+{
+  // "Color" objects gray by adding them to the mark stack for further processing.
+  //
+  // Note that stack objects are always colored red during creation, so
+  // they should never be added to the mark stack. Which would be bad because it
+  // could lead to stack corruption.
+  if (is_object_type(obj) && mark(obj) == gc_color_clear) {
+    mark_stack = vpbuffer_add(mark_stack, &mark_stack_len, mark_stack_i++, obj);
+#if GC_DEBUG_VERBOSE
+    fprintf(stderr, "mark gray parent = %p (%d) obj = %p\n", parent,
+            type_of(parent), obj);
+#endif
+  }
+}
+
 // TODO: seriously consider changing the mark() macro to color(),
 // and sync up the header variable. that would make all of this code
 // bit clearer...
@@ -1165,22 +1181,6 @@ void gc_mark_black(object obj)
   }
 }
 
-void gc_collector_mark_gray(object parent, object obj)
-{
-  // "Color" objects gray by adding them to the mark stack for further processing.
-  //
-  // Note that stack objects are always colored red during creation, so
-  // they should never be added to the mark stack. Which would be bad because it
-  // could lead to stack corruption.
-  if (is_object_type(obj) && mark(obj) == gc_color_clear) {
-    mark_stack = vpbuffer_add(mark_stack, &mark_stack_len, mark_stack_i++, obj);
-#if GC_DEBUG_VERBOSE
-    fprintf(stderr, "mark gray parent = %p (%d) obj = %p\n", parent,
-            type_of(parent), obj);
-#endif
-  }
-}
-
 void gc_empty_collector_stack()
 {
   // Mark stack is only used by the collector thread, so no sync needed
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index cc339a4b..f98a9ce9 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -628,7 +628,6 @@ void gc_mark_gray(gc_thread_data * thd, object obj);
 void gc_mark_gray2(gc_thread_data * thd, object obj);
 void gc_collector_trace();
 void gc_mark_black(object obj);
-void gc_collector_mark_gray(object parent, object obj);
 void gc_empty_collector_stack();
 void gc_handshake(gc_status_type s);
 void gc_post_handshake(gc_status_type s);