diff --git a/core/threaded/reactor_threaded.c b/core/threaded/reactor_threaded.c
index 6ebf6c8c6..a462dd77c 100644
--- a/core/threaded/reactor_threaded.c
+++ b/core/threaded/reactor_threaded.c
@@ -691,7 +691,7 @@ void _lf_initialize_start_tag(environment_t *env) {
     // Add reactions invoked at tag (0,0) (including startup reactions) to the reaction queue
     _lf_trigger_startup_reactions(env);
 
-#ifdef FEDERATED
+#if defined FEDERATED
     // If env is the environment for the top-level enclave, then initialize the federate.
     environment_t *top_level_env;
     _lf_get_environments(&top_level_env);
@@ -703,24 +703,21 @@ void _lf_initialize_start_tag(environment_t *env) {
         // Get a start_time from the RTI
         synchronize_with_other_federates(); // Resets start_time in federated execution according to the RTI.
     }
+
     // The start time will likely have changed. Adjust the current tag and stop tag.
     env->current_tag = (tag_t){.time = start_time, .microstep = 0u};
     if (duration >= 0LL) {
         // A duration has been specified. Recalculate the stop time.
        env->stop_tag = ((tag_t) {.time = start_time + duration, .microstep = 0});
     }
-#endif
 
     _lf_initialize_timers(env);
 
-    // If the stop_tag is (0,0), also insert the shutdown
-    // reactions. This can only happen if the timeout time
-    // was set to 0.
-    if (lf_tag_compare(env->current_tag, env->stop_tag) >= 0) {
-        _lf_trigger_shutdown_reactions(env);
-    }
+    // If we have a non-zero STA offset, then we need to allow messages to arrive
+    // prior to the start time.  To avoid spurious STP violations, we temporarily
+    // set the current time back by the STA offset.
+    env->current_tag = (tag_t){.time = start_time - _lf_fed_STA_offset, .microstep = 0u};
 
-#if defined FEDERATED
     // Call wait_until if federated. This is required because the startup procedure
     // in synchronize_with_other_federates() can decide on a new start_time that is
     // larger than the current physical time.
@@ -739,15 +736,25 @@ void _lf_initialize_start_tag(environment_t *env) {
     // Here we wait until the start time and also release the environment mutex.
     // this means that the other worker threads will be allowed to start. We need
     // this to avoid potential deadlock in federated startup.
-    while(!wait_until(env, start_time, &env->event_q_changed)) {};
-    LF_PRINT_DEBUG("Done waiting for start time " PRINTF_TIME ".", start_time);
-    LF_PRINT_DEBUG("Physical time is ahead of current time by " PRINTF_TIME ". This should be small.",
+    while(!wait_until(env, start_time + _lf_fed_STA_offset, &env->event_q_changed)) {};
+    LF_PRINT_DEBUG("Done waiting for start time + STA offset " PRINTF_TIME ".", start_time + _lf_fed_STA_offset);
+    LF_PRINT_DEBUG("Physical time is ahead of current time by " PRINTF_TIME 
+            ". This should be close to the STA offset.",
             lf_time_physical() - start_time);
 
-    // Each federate executes the start tag (which is the current
-    // tag). Inform the RTI of this if needed.
-    send_next_event_tag(env, env->current_tag, true);
-#endif
+    // Restore the current tag to match the start time.
+    env->current_tag = (tag_t){.time = start_time, .microstep = 0u};
+
+    // For messages that may have arrived while we were waiting, put
+    // reactions on the reaction queue.
+    _lf_pop_events(env);
+
+    // If the stop_tag is (0,0), also insert the shutdown
+    // reactions. This can only happen if the timeout time
+    // was set to 0.
+    if (lf_tag_compare(env->current_tag, env->stop_tag) >= 0) {
+        _lf_trigger_shutdown_reactions(env);
+    }
 
 #ifdef FEDERATED_DECENTRALIZED
     // In federated execution (at least under decentralized coordination),
@@ -759,7 +766,22 @@ void _lf_initialize_start_tag(environment_t *env) {
     // to be removed, if appropriate before proceeding to executing tag (0,0).
     _lf_wait_on_tag_barrier(env, (tag_t){.time=start_time,.microstep=0});
     spawn_staa_thread();
-#endif // FEDERATED_DECENTRALIZED
+
+#else // NOT FEDERATED_DECENTRALIZED
+    // Each federate executes the start tag (which is the current
+    // tag). Inform the RTI of this if needed.
+    send_next_event_tag(env, env->current_tag, true);
+#endif // NOT FEDERATED_DECENTRALIZED
+#else // NOT FEDERATED
+    _lf_initialize_timers(env);
+
+    // If the stop_tag is (0,0), also insert the shutdown
+    // reactions. This can only happen if the timeout time
+    // was set to 0.
+    if (lf_tag_compare(env->current_tag, env->stop_tag) >= 0) {
+        _lf_trigger_shutdown_reactions(env);
+    }
+#endif // NOT FEDERATED
 
     // Set the following boolean so that other thread(s), including federated threads,
     // know that the execution has started