diff --git a/PGBuild/Modules/TestUpgrade.pm b/PGBuild/Modules/TestUpgrade.pm
index 19b48b3..dfff17f 100644
--- a/PGBuild/Modules/TestUpgrade.pm
+++ b/PGBuild/Modules/TestUpgrade.pm
@@ -117,11 +117,16 @@ sub check
         @checklog = run_log($cmd);
     }
 
+    # Pre-2019 runs could create src/test/regress/regression.diffs.  Its
+    # inclusion is a harmless no-op for later runs; if another stage
+    # (e.g. make_check()) failed and created that file, the run ends before
+    # reaching this stage.
     my @logfiles = glob(
         "$self->{pgsql}/contrib/pg_upgrade/*.log
          $self->{pgsql}/contrib/pg_upgrade/log/*
          $self->{pgsql}/src/bin/pg_upgrade/*.log
          $self->{pgsql}/src/bin/pg_upgrade/log/*
+         $self->{pgsql}/src/bin/pg_upgrade/tmp_check/*/*.diffs
          $self->{pgsql}/src/test/regress/*.diffs"
     );
     foreach my $log (@logfiles)