diff --git a/b2/boom.c b/b2/boom.c
index 0a1cde8..3968aad 100644
--- a/b2/boom.c
+++ b/b2/boom.c
@@ -75,15 +75,15 @@ static void do_substitutions(void)
 static void usage(const char *name)
 {
 	fprintf(stderr,
-"usage: %s file [[-type] file ...] [-q var=value ...] ...\n\n"
+"usage: %s file [[-type] file ...] [(-q|-Q) var=value ...] ...\n\n"
 "  file types:\n"
 "  -c  characteristics\n"
 "  -i  inventory\n"
 "  -x  currency exchange\n"
 "  -p  providers\n"
 "  -s  substitutions\n"
-"  -q var=value ...\n"
-"  -Q var=value ...\n"
+"  -q var=value ...  run substitutions with the specified inputs\n"
+"  -Q var=value ...  run substitutions and then do parametric search\n"
     , name);
 	exit(1);
 }