diff --git a/src/clib/grackle_chemistry_data_fields.def b/src/clib/grackle_chemistry_data_fields.def
index bcc8aa4a..9124b3df 100644
--- a/src/clib/grackle_chemistry_data_fields.def
+++ b/src/clib/grackle_chemistry_data_fields.def
@@ -208,6 +208,10 @@ ENTRY(collisional_ionisation_rates, INT, 1) //Collisional ionisation
 ENTRY(recombination_cooling_rates, INT, 1) //Recombination cooling
 ENTRY(bremsstrahlung_cooling_rates, INT, 1) //Bremsstrahlung cooling
 
+/* Flag to specify unit-handling. Use the GR_UNIT_HANDLING_LEGACY and
+   GR_UNIT_HANDLING_AUTOMATIC to set the flag values */
+ENTRY(unit_handling, INT, -3)
+
 /* maximum number of subcycle iterations for solve_chemistry */
 ENTRY(max_iterations, INT, 10000)
 
diff --git a/src/clib/initialize_chemistry_data.c b/src/clib/initialize_chemistry_data.c
index ed51108b..f045f8d7 100644
--- a/src/clib/initialize_chemistry_data.c
+++ b/src/clib/initialize_chemistry_data.c
@@ -236,6 +236,21 @@ int local_initialize_chemistry_data(chemistry_data *my_chemistry,
 //omp_set_schedule( omp_sched_auto,    chunk_size );
 # endif
 
+  if (my_chemistry->unit_handling == -3) {
+    if (grackle_verbose) {
+      fprintf(stderr, ("WARNING: unit_handling is unset. Defaulting to legacy "
+                       "handling.\n"));
+    }
+    my_chemistry->unit_handling = GR_UNIT_HANDLING_LEGACY;
+  } else if ((my_chemistry->unit_handling != GR_UNIT_HANDLING_LEGACY) &&
+             (my_chemistry->unit_handling != GR_UNIT_HANDLING_AUTOMATIC)) {
+    fprintf(stderr, "unit_handling has an invalid value\n");
+    return GR_FAIL;
+  }
+
+  /* store a copy of the initial units */
+  my_rates->initial_units = *my_units;
+
   /* Only allow a units to be one with proper coordinates. */
   if (my_units->comoving_coordinates == FALSE &&
       my_units->a_units != 1.0) {
@@ -342,8 +357,6 @@ int local_initialize_chemistry_data(chemistry_data *my_chemistry,
     return GR_FAIL;
   }
 
-  /* store a copy of the initial units */
-  my_rates->initial_units = *my_units;
 
   if (grackle_verbose) {
     time_t timer;
diff --git a/src/include/grackle.h b/src/include/grackle.h
index 3796e787..14e1e3d5 100644
--- a/src/include/grackle.h
+++ b/src/include/grackle.h
@@ -26,6 +26,9 @@ extern "C" {
 #define GR_FAIL 0
 
 #define GR_SPECIFY_INITIAL_A_VALUE -1
+#define GR_UNIT_HANDLING_LEGACY -2
+#define GR_UNIT_HANDLING_AUTOMATIC -1
+
 
 extern int grackle_verbose;
 
diff --git a/src/include/grackle_chemistry_data.h b/src/include/grackle_chemistry_data.h
index 22ce5007..9a2cc223 100644
--- a/src/include/grackle_chemistry_data.h
+++ b/src/include/grackle_chemistry_data.h
@@ -176,6 +176,9 @@ typedef struct
   int recombination_cooling_rates; //Recombination cooling
   int bremsstrahlung_cooling_rates; //Bremsstrahlung cooling
 
+  /* Flag to specify unit-handling */
+  int unit_handling;
+
   /* maximum number of subcycle iterations for solve_chemistry */
   int max_iterations;