diff --git a/.gitignore b/.gitignore
index 9a81b694..4b9b03bd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -42,6 +42,9 @@ t/shim.log
 t/t0022-shim-random.sh
 t/tmptrace/
 t/trace
+# t/test-lib.sh keeps the trash directory when a test fails, so these linger
+# after every red run.
+t/trash-directory.*
 tmp/
 goodbye.ts
 version.ts
diff --git a/fixtures/workspace_flow/bootstrap.sh b/fixtures/workspace_flow/bootstrap.sh
index 06e1804a..d1b1dadc 100755
--- a/fixtures/workspace_flow/bootstrap.sh
+++ b/fixtures/workspace_flow/bootstrap.sh
@@ -21,6 +21,11 @@ init_repo() {
 	(
 		cd "$repo_dir"
 		git init -q
+		# Pin the branch rather than inheriting the host's default. Tests built
+		# on this fixture name `main`, and git still defaults to `master` where
+		# init.defaultBranch is unset. Setting HEAD while it is unborn works on
+		# every git version, unlike `git init -b`.
+		git symbolic-ref HEAD refs/heads/main
 		git config user.email "fixture@example.com"
 		git config user.name "Fixture User"
 		printf "%s\n" "$file_content" > "$file_name"