diff --git a/MCprep_addon/materials/prep.py b/MCprep_addon/materials/prep.py
index 4b08c146..04e7284c 100644
--- a/MCprep_addon/materials/prep.py
+++ b/MCprep_addon/materials/prep.py
@@ -250,7 +250,7 @@ def execute(self, context):
 					self.useReflections, 
 					self.usePrincipledShader, 
 					self.makeSolid, 
-					generate.PackFormatself.packFormat.upper(), 
+					generate.PackFormat[self.packFormat.upper()], 
 					self.useEmission, 
 					False # This is for an option set in matprep_cycles
 				)