diff --git a/configure/RULES_BUILD b/configure/RULES_BUILD
index 3f952c516..33db58662 100644
--- a/configure/RULES_BUILD
+++ b/configure/RULES_BUILD
@@ -325,7 +325,7 @@ tapfiles: $(TESTSCRIPTS) $(TAPFILES)
 
 # A .tap file is the output from running the associated test script
 %.tap: %.t
-	-HARNESS_ACTIVE=1 $(PERL) $< > $@
+	-$(PERL) $< -tap > $@
 
 # If there's a perl test script (.plt) available, use it
 %.t: ../%.plt
diff --git a/src/tools/makeTestfile.pl b/src/tools/makeTestfile.pl
index 80f6f4d38..a037eb71c 100644
--- a/src/tools/makeTestfile.pl
+++ b/src/tools/makeTestfile.pl
@@ -12,6 +12,8 @@
 # because some versions of the Perl test harness can only run test scripts
 # that are actually written in Perl.  The script we generate execs the
 # real test program which must be in the same directory as the .t file.
+# If the script is given an argument -tap it sets HARNESS_ACTIVE in the
+# environment to make the epicsUnitTest code generate strict TAP output.
 
 # Usage: makeTestfile.pl target.t executable
 #     target.t is the name of the Perl script to generate
@@ -25,6 +27,7 @@ open(my $OUT, '>', $target) or die "Can't create $target: $!\n";
 
 print $OUT <<EOF;
 #!/usr/bin/perl
+\$ENV{HARNESS_ACTIVE} = 1 if scalar \@ARGV && shift eq '-tap';
 exec './$exe' or die 'exec failed';
 EOF