diff --git a/binarycpython/utils/HPC.py b/binarycpython/utils/HPC.py
index ada6b0cc09aba174dcdef7bb8543aa7bc7afb7fc..13b16808102c8db86d0dd4c625179367b1f2fbd9 100644
--- a/binarycpython/utils/HPC.py
+++ b/binarycpython/utils/HPC.py
@@ -42,7 +42,7 @@ class HPC(condor,slurm):
             list = f.read().splitlines()
             f.close()
 
-            if self.grid_options['HPC_prepend_dir_to_joinlist'] = True:
+            if self.grid_options['HPC_prepend_dir_to_joinlist'] is True:
                 list = [os.path.join(prefix,file) for file in list]
         except:
             print("Failed to open joinlist at {list}".format(list=joinlist))