diff --git a/gc.c b/gc.c
index 3a60a96e234531..839c84e464466a 100644
--- a/gc.c
+++ b/gc.c
@@ -2666,10 +2666,6 @@ gc_event_hook_body(rb_execution_context_t *ec, rb_objspace_t *objspace, const rb
 
 #define gc_event_hook(objspace, event, data) gc_event_hook_prep(objspace, event, data, (void)0)
 
-#if USE_MMTK
-
-#endif
-
 static inline VALUE
 newobj_init(VALUE klass, VALUE flags, int wb_protected, rb_objspace_t *objspace, VALUE obj)
 {
@@ -3341,7 +3337,8 @@ cvar_table_free_i(VALUE value, void *ctx)
 #define ZOMBIE_OBJ_KEPT_FLAGS (FL_SEEN_OBJ_ID | FL_FINALIZE)
 
 #if USE_MMTK
-static inline void rb_mmtk_push_final_job(struct MMTk_FinalJob *job)
+static inline void
+rb_mmtk_push_final_job(struct MMTk_FinalJob *job)
 {
     rb_objspace_t *objspace = &rb_objspace;
 
@@ -7524,7 +7521,7 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
         if (any->as.match.str) {
             gc_mark(objspace, any->as.match.str);
         }
-        #if USE_MMTK
+#if USE_MMTK
         if (rb_mmtk_enabled_p()) {
             // If GC is triggered when the mutator is resizing the following buffers, we retain
             // them because their contents need to be copied to the new buffers after GC.
@@ -7532,7 +7529,7 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
             rb_mmtk_scan_offsetted_strbuf_field((char**)&RMATCH_EXT(any)->regs.beg, false);
             rb_mmtk_scan_offsetted_strbuf_field((char**)&RMATCH_EXT(any)->regs.end, false);
         }
-        #endif
+#endif
         break;
 
       case T_RATIONAL:
@@ -10321,7 +10318,7 @@ gc_sort_heap_by_compare_func(rb_objspace_t *objspace, gc_compact_compare_func co
 
 #if USE_MMTK
 static void
-gc_ref_update_string(rb_objspace_t * objspace, VALUE str)
+rb_mmtk_gc_ref_update_string(rb_objspace_t * objspace, VALUE str)
 {
      if (STR_EMBED_P(str)) {
         // Embedded strings don't point into any buffer.
@@ -10851,7 +10848,7 @@ gc_update_object_references(rb_objspace_t *objspace, VALUE obj)
         {
 #if USE_MMTK
             if (rb_mmtk_enabled_p()) {
-                gc_ref_update_string(objspace, obj);
+                rb_mmtk_gc_ref_update_string(objspace, obj);
                 break;
             }
 #endif
@@ -10926,7 +10923,7 @@ gc_update_object_references(rb_objspace_t *objspace, VALUE obj)
             UPDATE_IF_MOVED(objspace, any->as.match.str);
         }
 
-        #if USE_MMTK
+#if USE_MMTK
         if (rb_mmtk_enabled_p()) {
             // If GC is triggered when the mutator is resizing the following buffers, we retain
             // them because their contents need to be copied to the new buffers after GC.
@@ -10934,7 +10931,7 @@ gc_update_object_references(rb_objspace_t *objspace, VALUE obj)
             rb_mmtk_scan_offsetted_strbuf_field((char**)&RMATCH_EXT(any)->regs.beg, true);
             rb_mmtk_scan_offsetted_strbuf_field((char**)&RMATCH_EXT(any)->regs.end, true);
         }
-        #endif
+#endif
 
         break;
 
diff --git a/imemo.c b/imemo.c
index c6013e8bc7870a..7f30a2651eb65f 100644
--- a/imemo.c
+++ b/imemo.c
@@ -241,7 +241,7 @@ cc_table_mark_i(ID id, VALUE ccs_ptr, void *data)
 
 #if USE_MMTK
 static enum rb_id_table_iterator_result
-cc_table_mark_i_no_id(VALUE ccs_ptr, void *data_ptr)
+rb_mmtk_cc_table_mark_i_no_id(VALUE ccs_ptr, void *data_ptr)
 {
     return cc_table_mark_i(0, ccs_ptr, data_ptr);
 }
@@ -257,7 +257,7 @@ rb_cc_table_mark(VALUE klass)
             // Note: rb_id_table_foreach will look up the ID from keys by accessing
             // arrays in the heap during key2id, but the id is only used for
             // assertion which fails with an evacuating GC (such as Immix) anyway.
-            rb_id_table_foreach_values(cc_tbl, cc_table_mark_i_no_id, (void *)klass);
+            rb_id_table_foreach_values(cc_tbl, rb_mmtk_cc_table_mark_i_no_id, (void *)klass);
         } else {
 #endif
         rb_id_table_foreach(cc_tbl, cc_table_mark_i, (void *)klass);