diff --git a/sandbox/make_output_files.py b/sandbox/make_output_files.py
index fff74a8..f5604c6 100644
--- a/sandbox/make_output_files.py
+++ b/sandbox/make_output_files.py
@@ -81,7 +81,7 @@
 	output_string = output_string[:-2]
 	colour_string = colour_string[:-2]
 
-if args.heatmap is "F":
+if args.heatmap == "F":
 	print("heatmap script is not executed")
 
 command = "Rscript" # --vanilla --slave < "