diff --git a/gc.c b/gc.c
index e12886d7..67e5de3c 100644
--- a/gc.c
+++ b/gc.c
@@ -498,13 +498,12 @@ void gc_mark_gray(gc_thread_data *thd, object obj)
   // into the heap, with the collector being the only thread that changes marks. but double-check.
   if (is_object_type(obj) && mark(obj) == ATOMIC_GET(&gc_color_clear)) { // TODO: sync??
     // TODO: lock mark buffer (not ideal, but a possible first step)?
-    // pthread_mutex_lock
+    pthread_mutex_lock(&(thd->lock));
     thd->mark_buffer = vpbuffer_add(thd->mark_buffer, 
                                     &(thd->mark_buffer_len),
                                     thd->last_write,
                                     obj);
-    // pthread_mutex_unlock
-    // unlock mark buffer
+    pthread_mutex_unlock(&(thd->lock));
     ATOMIC_INC(&(thd->last_write));
   }
 }
@@ -526,6 +525,24 @@ void gc_col_empty_collector_stack()
 
 // END tri-color marking section
 
+
+// Initialize a thread from scratch
+void gc_thread_data_init(gc_thread_data *thd)
+{
+  thd->moveBufLen = 0;
+  gc_thr_grow_move_buffer(thd);
+// TODO: depends on collector state:  thd->gc_alloc_color = ATOMIC_GET(&gc_;
+// TODO: depends on collector state:  thd->gc_mut_status;
+  thd->last_write = 0;
+  thd->last_read = 0;
+  thd->mark_buffer_len = 128;
+  thd->mark_buffer = vpbuffer_realloc(thd->mark_buffer, &(thd->mark_buffer_len));
+  if (pthread_mutex(&(thd->lock), NULL) != 0) {
+    fprintf(stderr, "Unable to initialize thread mutex\n");
+    exit(1);
+  }
+}
+
 //// Unit testing:
 //int main(int argc, char **argv) {
 //  int a = 1, b = 2, c = 3, i;
diff --git a/include/cyclone/runtime-main.h b/include/cyclone/runtime-main.h
index ad98878a..5a4af9eb 100644
--- a/include/cyclone/runtime-main.h
+++ b/include/cyclone/runtime-main.h
@@ -59,9 +59,8 @@ static void Cyc_main (stack_size,heap_size,stack_base)
 
   Cyc_heap = gc_heap_create(heap_size / 2, 0, 0);
   //Cyc_heap = gc_heap_create(1024, 0, 0);
-  Cyc_thread = (gc_thread_data *)malloc(sizeof(gc_thread_data));
-  Cyc_thread->moveBufLen = 0;
-  gc_thr_grow_move_buffer(Cyc_thread); // Initialize the buffer
+  Cyc_thread = malloc(sizeof(gc_thread_data));
+  gc_thread_data_init(Cyc_thread);
   
 
   // JAE TODO: clean up below (and all of this old code, really)
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 631058cd..b83b80ef 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -16,6 +16,7 @@
 #include <stdarg.h>
 #include <string.h>
 #include <math.h>
+#include <pthread.h>
 
 /* Define general object type. */
 typedef void *object;
@@ -32,6 +33,7 @@ struct gc_thread_data_t {
   int last_read;
   void **mark_buffer;
   int mark_buffer_len;
+  pthread_mutex_t lock;
 };
 
 /* GC data structures */
@@ -91,6 +93,7 @@ size_t gc_sweep(gc_heap *h, size_t *sum_freed_ptr);
 size_t gc_collect(gc_heap *h, size_t *sum_freed);
 void gc_thr_grow_move_buffer(gc_thread_data *d);
 void gc_thr_add_to_move_buffer(gc_thread_data *d, int *alloci, object obj);
+void gc_thread_data_init(gc_thread_data *thd);
 
 /* GC debugging flags */
 //#define DEBUG_GC 0