diff --git a/gprMax/hash_cmds_singleuse.py b/gprMax/hash_cmds_singleuse.py
index 6dd3765b..76456174 100644
--- a/gprMax/hash_cmds_singleuse.py
+++ b/gprMax/hash_cmds_singleuse.py
@@ -121,6 +121,7 @@ def process_singlecmds(singlecmds):
         scene_objects.append(tw)
 
     cmd = "#pml_formulation"
+    pml_formulation = None
     if singlecmds[cmd] is not None:
         tmp = singlecmds[cmd].split()
         if len(tmp) != 1:
@@ -135,19 +136,16 @@ def process_singlecmds(singlecmds):
         if len(tmp) not in [1, 6]:
             logger.exception(f"{cmd} requires either one or six parameter(s)")
             raise ValueError
-        if pml_formulation:
-            formulation = pml_formulation
-        else:
-            formulation = None
+        
         if len(tmp) == 1:
-            pml_cells = PMLProps(formulation=formulation, thickness=int(tmp[0]))
+            pml_cells = PMLProps(formulation=pml_formulation, thickness=int(tmp[0]))
         else:
             pml_cells = PMLProps(
-                formulation=formulation, 
+                formulation=pml_formulation, 
                 x0=int(tmp[0]), y0=int(tmp[1]), z0=int(tmp[2]), 
                 xmax=int(tmp[3]), ymax=int(tmp[4]), zmax=int(tmp[5])
             )
-
+            
         scene_objects.append(pml_cells)
 
     cmd = "#src_steps"