diff --git a/gc.c b/gc.c
index be4bc20d..04eb126a 100644
--- a/gc.c
+++ b/gc.c
@@ -17,8 +17,6 @@
 ////////////////////
 // Global variables
 
-static const int NANOSECONDS_PER_MILLISECOND = 1000000;
-
 // Note: will need to use atomics and/or locking to access any
 // variables shared between threads
 static int        gc_color_mark = 1; // Black, is swapped during GC
diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 30cbe7a1..7a2aa7a4 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -189,6 +189,7 @@ object memqp(void *,object,list);
 object Cyc_spawn_thread(object thunk);
 void Cyc_start_thread(gc_thread_data *thd);
 void Cyc_end_thread(gc_thread_data *thd);
+object Cyc_thread_sleep(void *data, object timeout);
 void GC(void *,closure,object*,int);
 
 void Cyc_st_add(void *data, char *frame);
@@ -228,6 +229,7 @@ extern const object primitive_Cyc_91cvar_127;
 extern const object primitive_Cyc_91has_91cycle_127;
 extern const object primitive_Cyc_91spawn_91thread_67;
 extern const object primitive_Cyc_91end_91thread_67;
+extern const object primitive_Cyc_91thread_91sleep_67;
 extern const object primitive__87;
 extern const object primitive__91;
 extern const object primitive__85;
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 26e05d82..7d3b7006 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -43,6 +43,8 @@
    necessary if GC is working correctly. */
 #define GC_SAFETY_CHECKS 1
 
+// General constants
+#define NANOSECONDS_PER_MILLISECOND 1000000
 
 /* Define general object type. */
 typedef void *object;
diff --git a/runtime.c b/runtime.c
index a908eecb..77a4132d 100644
--- a/runtime.c
+++ b/runtime.c
@@ -1709,6 +1709,9 @@ void _Cyc_91spawn_91thread_67(void *data, object cont, object args) {
 void _Cyc_91end_91thread_67(void *data, object cont, object args) {
     Cyc_end_thread((gc_thread_data *)data);
     return_closcall1(data, cont, boolean_f); }
+void _Cyc_91thread_91sleep_67(void *data, object cont, object args) {
+    Cyc_check_num_args(data, "Cyc-thread-sleep!", 1, args);
+    return_closcall1(data, cont, Cyc_thread_sleep(data, car(args))); }
 void __87(void *data, object cont, object args) {
     integer_type argc = Cyc_length(data, args);
     dispatch(data, argc.value, (function_type)dispatch_sum, cont, cont, args); }
@@ -2900,6 +2903,7 @@ static primitive_type Cyc_91cvar_127_primitive = {{0}, primitive_tag, "Cyc-cvar?
 static primitive_type Cyc_91has_91cycle_127_primitive = {{0}, primitive_tag, "Cyc-has-cycle?", &_Cyc_91has_91cycle_127};
 static primitive_type Cyc_91spawn_91thread_67_primitive = {{0}, primitive_tag, "Cyc-spawn-thread!", &_Cyc_91spawn_91thread_67};
 static primitive_type Cyc_91end_91thread_67_primitive = {{0}, primitive_tag, "Cyc-end-thread!", &_Cyc_91end_91thread_67};
+static primitive_type Cyc_91thread_91sleep_67_primitive = {{0}, primitive_tag, "Cyc-thread-sleep!", &_Cyc_91thread_91sleep_67};
 static primitive_type _87_primitive = {{0}, primitive_tag, "+", &__87};
 static primitive_type _91_primitive = {{0}, primitive_tag, "-", &__91};
 static primitive_type _85_primitive = {{0}, primitive_tag, "*", &__85};
@@ -3019,6 +3023,7 @@ const object primitive_Cyc_91cvar_127 = &Cyc_91cvar_127_primitive;
 const object primitive_Cyc_91has_91cycle_127 = &Cyc_91has_91cycle_127_primitive;
 const object primitive_Cyc_91spawn_91thread_67 = &Cyc_91spawn_91thread_67_primitive;
 const object primitive_Cyc_91end_91thread_67 = &Cyc_91end_91thread_67_primitive;
+const object primitive_Cyc_91thread_91sleep_67 = &Cyc_91thread_91sleep_67_primitive;
 const object primitive__87 = &_87_primitive;
 const object primitive__91 = &_91_primitive;
 const object primitive__85 = &_85_primitive;
@@ -3203,3 +3208,14 @@ void Cyc_end_thread(gc_thread_data *thd)
   pthread_exit(NULL); // For now, just a proof of concept
 }
 
+// For now, accept a number of milliseconds to sleep
+object Cyc_thread_sleep(void *data, object timeout)
+{
+  struct timespec tim;
+  Cyc_check_num(data, timeout);
+  tim.tv_sec = 0;
+  tim.tv_nsec = ((integer_type *)timeout)->value * NANOSECONDS_PER_MILLISECOND;
+  nanosleep(&tim, NULL);
+  return boolean_t;
+}
+