diff --git a/trace/gen.bash b/trace/gen.bash
index 6dcaafd..fc5445d 100755
--- a/trace/gen.bash
+++ b/trace/gen.bash
@@ -34,7 +34,7 @@
 DST=$(dirname $0)
 
 # Copy.
-cp -r $SRC/* $DST
+rsync -av --delete $SRC/ $DST
 rm $DST/mkexp.bash
 
 # Remove the trace_test.go file and the testprogs it invokes.
@@ -46,6 +46,13 @@
 rm $DST/trace_test.go
 rm -r $DST/testdata/testprog
 
+# Remove the oldtrace testdata to avoid checking in new binary files.
+# Remove oldtrace_test.go and internal/oldtrace/parser_test.go because
+# they fail without this data.
+rm -r $DST/internal/oldtrace/testdata
+rm $DST/oldtrace_test.go
+rm $DST/internal/oldtrace/parser_test.go
+
 # Remove mktests.go because its a //go:build ignore file, so it would
 # complicate the logic below. This codebase isn't the source of truth
 # anyway.
@@ -76,3 +83,6 @@
 
 # Format the files.
 find $DST -name '*.go' | xargs -- gofmt -w -s
+
+# Restore known files.
+git checkout gen.bash flightrecorder.go flightrecorder_test.go