lib/PublicInbox/SearchIdx.pm | 4 +++-

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 21ab8119e70fe559fbe5435fea50a443b0b1459a..4cfbc4aae36577f87ec11191ff2f9e4dfd7d2f5d 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -255,7 +255,9 @@ 				/^\\ No newline at end of file/ ||
 				/^Binary files .* differ/) {
 			push @xnq, $_;
 		} elsif ($_ eq '') {
-			$in_diff = undef;
+			# possible to be in diff context, some mail may be
+			# stripped by MUA or even GNU diff(1).  "git apply"
+			# treats a bare "\n" as diff context, too
 		} else {
 			push @xnq, $_;
 			warn "non-diff line: $_\n" if DEBUG && $_ ne '';