diff --git a/include/cyclone/runtime-main.h b/include/cyclone/runtime-main.h
index c99cee8b..3d1890e8 100644
--- a/include/cyclone/runtime-main.h
+++ b/include/cyclone/runtime-main.h
@@ -19,10 +19,6 @@ static void Cyc_heap_init(long heap_size);
 
 static void Cyc_heap_init(long heap_size)
 {
-  /* Initialize stack trace table
-     TODO: will eventually be relocated to a per-thread operation */
-  Cyc_st_init();
-
   /* Allocate heap area for second generation. */
 #if DEBUG_SHOW_DIAG
   printf("main: Allocating and initializing heap...\n");
diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 919101db..b1888bcb 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -189,9 +189,9 @@ object memqp(void *,object,list);
 void Cyc_start_thread(gc_thread_data *thd);
 void GC(void *,closure,object*,int);
 
-void Cyc_st_init();
 void Cyc_st_add(char *frame);
-void Cyc_st_print(FILE *out);
+void Cyc_st_add2(void *data, char *frame);
+void Cyc_st_print(void *data, FILE *out);
 
 char *_strdup (const char *s);
 object add_symbol(symbol_type *psym);
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 1b51e7b7..3d423096 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -60,6 +60,10 @@ struct gc_thread_data_t {
   void **mark_buffer;
   int mark_buffer_len;
   pthread_mutex_t lock;
+  // Data needed for call history
+  char **stack_traces;
+  int stack_trace_idx;
+  char *stack_prev_frame;
 };
 
 /* GC data structures */
diff --git a/runtime.c b/runtime.c
index 1a1cbcce..e5b1aea9 100644
--- a/runtime.c
+++ b/runtime.c
@@ -189,24 +189,19 @@ const object quote_void = &Cyc_void_symbol;
 
 /* Stack Traces */
 static const int MAX_STACK_TRACES = 10;
-static char **Cyc_Stack_Traces;
-static int Cyc_Stack_Trace_Idx = 0;
-static char *Cyc_Stack_Prev_Frame = NULL;
 
-void Cyc_st_init() { 
-  Cyc_Stack_Traces = calloc(MAX_STACK_TRACES, sizeof(char *));
-}
-
-void Cyc_st_add(char *frame) { 
+void Cyc_st_add(char *frame) { } // TODO: a temporary function, merge with below
+void Cyc_st_add2(void *data, char *frame) { 
+  gc_thread_data *thd = (gc_thread_data *)data;
   // Do not allow recursion to remove older frames
-  if (frame != Cyc_Stack_Prev_Frame) { 
-    Cyc_Stack_Prev_Frame = frame;
-    Cyc_Stack_Traces[Cyc_Stack_Trace_Idx] = frame;
-    Cyc_Stack_Trace_Idx = (Cyc_Stack_Trace_Idx + 1) % MAX_STACK_TRACES;
+  if (frame != thd->stack_prev_frame) { 
+    thd->stack_prev_frame = frame;
+    thd->stack_traces[thd->stack_trace_idx] = frame;
+    thd->stack_trace_idx = (thd->stack_trace_idx + 1) % MAX_STACK_TRACES;
   }
 }
 
-void Cyc_st_print(FILE *out) {
+void Cyc_st_print(void *data, FILE *out) {
   /* print to stream, note it is possible that
      some traces could be on the stack after a GC.
      not sure what to do about it, may need to
@@ -214,10 +209,11 @@ void Cyc_st_print(FILE *out) {
      or, with the tbl being so small, maybe it will
      not be an issue in practice? a bit risky to ignore though
   */
-  int i = (Cyc_Stack_Trace_Idx + 1) % MAX_STACK_TRACES;
-  while (i != Cyc_Stack_Trace_Idx) {
-    if (Cyc_Stack_Traces[i]) {
-      fprintf(out, "%s\n", Cyc_Stack_Traces[i]);
+  gc_thread_data *thd = (gc_thread_data *)data;
+  int i = (thd->stack_trace_idx + 1) % MAX_STACK_TRACES;
+  while (i != thd->stack_trace_idx) {
+    if (thd->stack_traces[i]) {
+      fprintf(out, "%s\n", thd->stack_traces[i]);
     }
     i = (i + 1) % MAX_STACK_TRACES;
   }
@@ -361,7 +357,7 @@ object Cyc_default_exception_handler(void *data, int argc, closure _, object err
     }
 
     fprintf(stderr, "\nCall history:\n");
-    Cyc_st_print(stderr);
+    Cyc_st_print(data, stderr);
     fprintf(stderr, "\n");
     //raise(SIGINT); // break into debugger, unix only
     exit(1);
@@ -2484,6 +2480,13 @@ void Cyc_apply_from_buf(void *data, int argc, object prim, object *buf) {
 
 void Cyc_start_thread(gc_thread_data *thd)
 {
+  thd->stack_trace_idx = 0;
+  thd->stack_prev_frame = NULL;
+  // TODO: may need to relocate the calloc to another function that
+  // initializes thread objects, rather than here that just calls them.
+  // at a minimum, should initialize it to NULL so we can test for that here.
+  thd->stack_traces = calloc(MAX_STACK_TRACES, sizeof(char *));
+
   /* Tank, load the jump program... */
   setjmp(*(thd->jmp_start));
 
diff --git a/scheme/cyclone/cgen.sld b/scheme/cyclone/cgen.sld
index 9ebbf111..76c4d567 100644
--- a/scheme/cyclone/cgen.sld
+++ b/scheme/cyclone/cgen.sld
@@ -183,7 +183,7 @@
           (null? (cdr trace)))
     ""
     (string-append 
-      "Cyc_st_add(\""
+      "Cyc_st_add2(data, \""
       (car trace) 
       ":" 
       ;; TODO: escape backslashes