diff --git a/src/tools/msvc/vcregress.pl b/src/tools/msvc/vcregress.pl
index d73775c743018f224359c48881819a1f9a95f620..bfa8a3dc909935dfa2a8f56b284873b8e7793a87 100644
--- a/src/tools/msvc/vcregress.pl
+++ b/src/tools/msvc/vcregress.pl
@@ -410,7 +410,7 @@ sub fetchRegressOpts
 	my @opts;
 
 	$m =~ s{\\\r?\n}{}g;
-	if ($m =~ /^\s*REGRESS_OPTS\s*=(.*)/m)
+	if ($m =~ /^\s*REGRESS_OPTS\s*\+?=(.*)/m)
 	{
 		# Substitute known Makefile variables, then ignore options that retain
 		# an unhandled variable reference.  Ignore anything that isn't an