diff -Nru dpkg-1.20.5ubuntu2/debian/changelog dpkg-1.20.5ubuntu3/debian/changelog
--- dpkg-1.20.5ubuntu2/debian/changelog	2020-08-31 02:34:46.000000000 +0200
+++ dpkg-1.20.5ubuntu3/debian/changelog	2020-10-16 21:18:40.000000000 +0200
@@ -1,3 +1,11 @@
+dpkg (1.20.5ubuntu3) groovy; urgency=medium
+
+  * scripts/Dpkg/Vendor/Ubuntu.pm, scripts/dpkg-buildpackage.pl:
+    Set 'nocheck' for riscv64 using a new 'update-buildopts' hook and make it
+    effective with old style debhelper, too.
+
+ -- Balint Reczey <rbalint@ubuntu.com>  Fri, 16 Oct 2020 21:18:40 +0200
+
 dpkg (1.20.5ubuntu2) groovy; urgency=medium
 
   * scripts/Dpkg/Vendor/Ubuntu.pm: set 'nocheck' in build options by default
diff -Nru dpkg-1.20.5ubuntu2/scripts/Dpkg/Vendor/Ubuntu.pm dpkg-1.20.5ubuntu3/scripts/Dpkg/Vendor/Ubuntu.pm
--- dpkg-1.20.5ubuntu2/scripts/Dpkg/Vendor/Ubuntu.pm	2020-08-30 23:06:54.000000000 +0200
+++ dpkg-1.20.5ubuntu3/scripts/Dpkg/Vendor/Ubuntu.pm	2020-10-16 21:18:40.000000000 +0200
@@ -92,6 +92,14 @@
             $fields->{'Launchpad-Bugs-Fixed'} = join(' ', @$bugs);
         }
 
+    } elsif ($hook eq 'update-buildopts') {
+	my $build_opts = shift @params;
+	require Dpkg::Arch;
+	my $arch = Dpkg::Arch::get_host_arch();
+	if (Dpkg::Arch::debarch_eq($arch, 'riscv64')) {
+	    $build_opts->set('nocheck', 1, 'riscv64');
+	}
+
     } elsif ($hook eq 'update-buildflags') {
 	my $flags = shift @params;
 
@@ -99,18 +107,12 @@
         $self->SUPER::run_hook($hook, $flags);
 
         require Dpkg::BuildOptions;
-	require Dpkg::Arch;
 
 	my $build_opts = Dpkg::BuildOptions->new();
-	my $arch = Dpkg::Arch::get_host_arch();
-
-	# disable build-time tests by default on riscv64; LP: #1891686
-	if (Dpkg::Arch::debarch_eq($arch, 'riscv64')) {
-	    $build_opts->merge('nocheck', 'riscv64');
-	    $build_opts->export();
-	}
 
 	if (!$build_opts->has('noopt')) {
+            require Dpkg::Arch;
+
             my $arch = Dpkg::Arch::get_host_arch();
             if (Dpkg::Arch::debarch_eq($arch, 'ppc64el')) {
 		for my $flag (qw(CFLAGS CXXFLAGS OBJCFLAGS OBJCXXFLAGS GCJFLAGS
diff -Nru dpkg-1.20.5ubuntu2/scripts/dpkg-buildpackage.pl dpkg-1.20.5ubuntu3/scripts/dpkg-buildpackage.pl
--- dpkg-1.20.5ubuntu2/scripts/dpkg-buildpackage.pl	2020-06-02 04:51:37.000000000 +0200
+++ dpkg-1.20.5ubuntu3/scripts/dpkg-buildpackage.pl	2020-10-16 21:18:40.000000000 +0200
@@ -203,6 +203,8 @@
 
 my $build_opts = Dpkg::BuildOptions->new();
 
+run_vendor_hook('update-buildopts', $build_opts);
+
 if ($build_opts->has('nocheck')) {
     $check_command = undef;
 } elsif (not find_command($check_command)) {
@@ -426,6 +428,8 @@
     }
     $build_opts->set('parallel', $parallel);
     $build_opts->export();
+} else {
+    $build_opts->export();
 }
 
 set_build_profiles(@build_profiles) if @build_profiles;