lib/PublicInbox/View.pm     | 4 +++-
 lib/PublicInbox/ViewDiff.pm | 6 ++++++

diff --git a/lib/PublicInbox/View.pm b/lib/PublicInbox/View.pm
index 47a2046e43da31d8533268a56ad6c4d290e50168..35e171b06959e364437c3f884919cd4e8439b104 100644
--- a/lib/PublicInbox/View.pm
+++ b/lib/PublicInbox/View.pm
@@ -568,7 +568,9 @@
 	# always support diff-highlighting, but we can't linkify hunk
 	# headers for solver unless some coderepo are configured:
 	my $diff;
-	if ($s =~ /^(?:diff|---|\+{3}) /ms) {
+	if ($s =~ /^([ \t]*)(?:diff|---|\+{3}) /ms) {
+		$ctx->{-dpfx} = $1 if $1; # for format-patch --interdiff output
+
 		# diffstat anchors do not link across attachments or messages:
 		$idx[0] = $upfx . $idx[0] if $upfx ne '';
 		$ctx->{-apfx} = join('/', @idx);
diff --git a/lib/PublicInbox/ViewDiff.pm b/lib/PublicInbox/ViewDiff.pm
index 6b8d94372405486ca2223e0fc057e79cb24691ac..e9cfc3687ba392f2858f7570908196af75163e2f 100644
--- a/lib/PublicInbox/ViewDiff.pm
+++ b/lib/PublicInbox/ViewDiff.pm
@@ -141,8 +141,14 @@ 	my $diff = $ctx->{-diff};
 	my $spfx = $ctx->{-spfx};
 	my $state = DSTATE_INIT;
 	my $dctx = { Q => '' }; # {}, keys: oid_a, oid_b, path_a, path_b
+	my $dpfx = $ctx->{-dpfx}; # leading spaces for interdiff
+	my $dpfx_re = qr/\A$dpfx/ if defined $dpfx;
 
 	foreach my $s (@$diff) {
+		if (defined($dpfx)) {
+			$s =~ s/$dpfx_re//;
+			$$dst .= $dpfx;
+		}
 		if ($s =~ /^---$/) {
 			to_state($dst, $state, DSTATE_STAT);
 			$$dst .= $s;