diff --git a/core/reactor_common.c b/core/reactor_common.c
index 8492ef48a..bd9cc1210 100644
--- a/core/reactor_common.c
+++ b/core/reactor_common.c
@@ -1325,3 +1325,8 @@ void termination(void) {
     }
     lf_tracing_global_shutdown();
 }
+
+index_t lf_combine_deadline_and_level(interval_t deadline, int level) {
+    if (deadline > ULLONG_MAX >> 16) return ((ULLONG_MAX >> 16) << 16) | level;
+    else return (deadline << 16) | level;
+}
diff --git a/include/core/reactor_common.h b/include/core/reactor_common.h
index 97ec976b8..92630be1e 100644
--- a/include/core/reactor_common.h
+++ b/include/core/reactor_common.h
@@ -65,6 +65,16 @@ extern struct allocation_record_t* _lf_reactors_to_free;
 
 //////////////////////  Functions  //////////////////////
 
+/**
+ * @brief Combine a deadline and a level into a single index for sorting in the reaction queue.
+ * 
+ * This shifts the deadline right by 16 bits and inserts the level in the low-order 16 bits.
+ * If the deadline is larger than `ULLONG_MAX >> 16`, then it is treated as the largest possible deadline.
+ * @oaran deadline THe deadline.
+ * @param level The level in the reaction graph.
+*/
+index_t lf_combine_deadline_and_level(interval_t deadline, int level);
+
 /**
  * @brief Create and initialize the required number of environments for the program.
  * @note This function will be code generated by the compiler.