diff --git a/gstlal-inspiral/bin/gstlal_inspiral_create_prior_diststats b/gstlal-inspiral/bin/gstlal_inspiral_create_prior_diststats
index 5088bf1704a7b58702f63198bc31d7ed38ac7571..165aaee9d0571598e01304bfd620718e0357c661 100755
--- a/gstlal-inspiral/bin/gstlal_inspiral_create_prior_diststats
+++ b/gstlal-inspiral/bin/gstlal_inspiral_create_prior_diststats
@@ -80,9 +80,9 @@ def parse_command_line():
 
 	process_params = dict(options.__dict__)
 
-	options.instrument = set(options.instrument)
 	if not options.instrument:
 		raise ValueError("must specify at least one --instrument")
+	options.instrument = set(options.instrument)
 
 	if options.min_instruments < 1:
 		raise ValueError("--min-instruments must be >= 1")