diff --git a/dev-infra/pr/discover-new-conflicts/index.ts b/dev-infra/pr/discover-new-conflicts/index.ts
index daa1873092..790d809438 100644
--- a/dev-infra/pr/discover-new-conflicts/index.ts
+++ b/dev-infra/pr/discover-new-conflicts/index.ts
@@ -63,8 +63,8 @@ export async function discoverNewConflictsForPr(
     process.exit(1);
   }
 
-  /** The active github branch when the run began. */
-  const originalBranch = git.getCurrentBranch();
+  /** The active github branch or revision before we performed any Git commands. */
+  const previousBranchOrRevision = git.getCurrentBranchOrRevision();
   /* Progress bar to indicate progress. */
   const progressBar = new Bar({format: `[{bar}] ETA: {eta}s | {value}/{total}`});
   /* PRs which were found to be conflicting. */
@@ -103,7 +103,7 @@ export async function discoverNewConflictsForPr(
   const result = exec(`git rebase FETCH_HEAD`);
   if (result.code) {
     error('The requested PR currently has conflicts');
-    cleanUpGitState(originalBranch);
+    cleanUpGitState(previousBranchOrRevision);
     process.exit(1);
   }
 
@@ -130,7 +130,7 @@ export async function discoverNewConflictsForPr(
   info();
   info(`Result:`);
 
-  cleanUpGitState(originalBranch);
+  cleanUpGitState(previousBranchOrRevision);
 
   // If no conflicts are found, exit successfully.
   if (conflicts.length === 0) {
@@ -147,14 +147,14 @@ export async function discoverNewConflictsForPr(
   process.exit(1);
 }
 
-/** Reset git back to the provided branch. */
-export function cleanUpGitState(branch: string) {
+/** Reset git back to the provided branch or revision. */
+export function cleanUpGitState(previousBranchOrRevision: string) {
   // Ensure that any outstanding rebases are aborted.
   exec(`git rebase --abort`);
   // Ensure that any changes in the current repo state are cleared.
   exec(`git reset --hard`);
   // Checkout the original branch from before the run began.
-  exec(`git checkout ${branch}`);
+  exec(`git checkout ${previousBranchOrRevision}`);
   // Delete the generated branch.
   exec(`git branch -D ${tempWorkingBranch}`);
 }
diff --git a/dev-infra/pr/merge/strategies/autosquash-merge.ts b/dev-infra/pr/merge/strategies/autosquash-merge.ts
index 198eda3daf..e304ed98bd 100644
--- a/dev-infra/pr/merge/strategies/autosquash-merge.ts
+++ b/dev-infra/pr/merge/strategies/autosquash-merge.ts
@@ -59,7 +59,7 @@ export class AutosquashMergeStrategy extends MergeStrategy {
     // is desired, we set the `GIT_SEQUENCE_EDITOR` environment variable to `true` so that
     // the rebase seems interactive to Git, while it's not interactive to the user.
     // See: https://github.com/git/git/commit/891d4a0313edc03f7e2ecb96edec5d30dc182294.
-    const branchBeforeRebase = this.git.getCurrentBranch();
+    const branchOrRevisionBeforeRebase = this.git.getCurrentBranchOrRevision();
     const rebaseEnv =
         needsCommitMessageFixup ? undefined : {...process.env, GIT_SEQUENCE_EDITOR: 'true'};
     this.git.run(
@@ -69,9 +69,9 @@ export class AutosquashMergeStrategy extends MergeStrategy {
     // Update pull requests commits to reference the pull request. This matches what
     // Github does when pull requests are merged through the Web UI. The motivation is
     // that it should be easy to determine which pull request contained a given commit.
-    // **Note**: The filter-branch command relies on the working tree, so we want to make
-    // sure that we are on the initial branch where the merge script has been run.
-    this.git.run(['checkout', '-f', branchBeforeRebase]);
+    // Note: The filter-branch command relies on the working tree, so we want to make sure
+    // that we are on the initial branch or revision where the merge script has been invoked.
+    this.git.run(['checkout', '-f', branchOrRevisionBeforeRebase]);
     this.git.run(
         ['filter-branch', '-f', '--msg-filter', `${MSG_FILTER_SCRIPT} ${prNumber}`, revisionRange]);
 
diff --git a/dev-infra/pr/merge/task.ts b/dev-infra/pr/merge/task.ts
index e02815cbc0..5a17784738 100644
--- a/dev-infra/pr/merge/task.ts
+++ b/dev-infra/pr/merge/task.ts
@@ -87,14 +87,14 @@ export class PullRequestMergeTask {
         new GithubApiMergeStrategy(this.git, this.config.githubApiMerge) :
         new AutosquashMergeStrategy(this.git);
 
-    // Branch that is currently checked out so that we can switch back to it once
-    // the pull request has been merged.
-    let previousBranch: null|string = null;
+    // Branch or revision that is currently checked out so that we can switch back to
+    // it once the pull request has been merged.
+    let previousBranchOrRevision: null|string = null;
 
     // The following block runs Git commands as child processes. These Git commands can fail.
     // We want to capture these command errors and return an appropriate merge request status.
     try {
-      previousBranch = this.git.getCurrentBranch();
+      previousBranchOrRevision = this.git.getCurrentBranchOrRevision();
 
       // Run preparations for the merge (e.g. fetching branches).
       await strategy.prepare(pullRequest);
@@ -107,7 +107,7 @@ export class PullRequestMergeTask {
 
       // Switch back to the previous branch. We need to do this before deleting the temporary
       // branches because we cannot delete branches which are currently checked out.
-      this.git.run(['checkout', '-f', previousBranch]);
+      this.git.run(['checkout', '-f', previousBranchOrRevision]);
 
       await strategy.cleanup(pullRequest);
 
@@ -123,8 +123,8 @@ export class PullRequestMergeTask {
     } finally {
       // Always try to restore the branch if possible. We don't want to leave
       // the repository in a different state than before.
-      if (previousBranch !== null) {
-        this.git.runGraceful(['checkout', '-f', previousBranch]);
+      if (previousBranchOrRevision !== null) {
+        this.git.runGraceful(['checkout', '-f', previousBranchOrRevision]);
       }
     }
   }
diff --git a/dev-infra/pr/rebase/index.ts b/dev-infra/pr/rebase/index.ts
index 0b9fa9fe77..8c0af93324 100644
--- a/dev-infra/pr/rebase/index.ts
+++ b/dev-infra/pr/rebase/index.ts
@@ -50,10 +50,10 @@ export async function rebasePr(
   }
 
   /**
-   * The branch originally checked out before this method performs any Git
-   * operations that may change the working branch.
+   * The branch or revision originally checked out before this method performed
+   * any Git operations that may change the working branch.
    */
-  const originalBranch = git.getCurrentBranch();
+  const previousBranchOrRevision = git.getCurrentBranchOrRevision();
   /* Get the PR information from Github. */
   const pr = await getPr(PR_SCHEMA, prNumber, config.github);
 
@@ -121,7 +121,7 @@ export async function rebasePr(
     info();
     info(`To abort the rebase and return to the state of the repository before this command`);
     info(`run the following command:`);
-    info(` $ git rebase --abort && git reset --hard && git checkout ${originalBranch}`);
+    info(` $ git rebase --abort && git reset --hard && git checkout ${previousBranchOrRevision}`);
     process.exit(1);
   } else {
     info(`Cleaning up git state, and restoring previous state.`);
@@ -137,7 +137,7 @@ export async function rebasePr(
     // Ensure that any changes in the current repo state are cleared.
     git.runGraceful(['reset', '--hard'], {stdio: 'ignore'});
     // Checkout the original branch from before the run began.
-    git.runGraceful(['checkout', originalBranch], {stdio: 'ignore'});
+    git.runGraceful(['checkout', previousBranchOrRevision], {stdio: 'ignore'});
   }
 }
 
diff --git a/dev-infra/utils/git/index.ts b/dev-infra/utils/git/index.ts
index dbfb50c180..3a15b5a098 100644
--- a/dev-infra/utils/git/index.ts
+++ b/dev-infra/utils/git/index.ts
@@ -119,9 +119,16 @@ export class GitClient {
     return this.run(['branch', branchName, '--contains', sha]).stdout !== '';
   }
 
-  /** Gets the currently checked out branch. */
-  getCurrentBranch(): string {
-    return this.run(['rev-parse', '--abbrev-ref', 'HEAD']).stdout.trim();
+  /** Gets the currently checked out branch or revision. */
+  getCurrentBranchOrRevision(): string {
+    const branchName = this.run(['rev-parse', '--abbrev-ref', 'HEAD']).stdout.trim();
+    // If no branch name could be resolved. i.e. `HEAD` has been returned, then Git
+    // is currently in a detached state. In those cases, we just want to return the
+    // currently checked out revision/SHA.
+    if (branchName === 'HEAD') {
+      return this.run(['rev-parse', 'HEAD']).stdout.trim();
+    }
+    return branchName;
   }
 
   /** Gets whether the current Git repository has uncommitted changes. */