diff --git a/server/events/vcs/instrumented_client.go b/server/events/vcs/instrumented_client.go
index d5d5809d9c..36aaf9b605 100644
--- a/server/events/vcs/instrumented_client.go
+++ b/server/events/vcs/instrumented_client.go
@@ -206,6 +206,12 @@ func (c *InstrumentedClient) PullIsMergeable(logger logging.SimpleLogging, repo
 }
 
 func (c *InstrumentedClient) UpdateStatus(logger logging.SimpleLogging, repo models.Repo, pull models.PullRequest, state models.CommitStatus, src string, description string, url string) error {
+	// If the plan isn't coming from a pull request,
+	// don't attempt to update the status.
+	if pull.Num == 0 {
+		return nil
+	}
+
 	scope := c.StatsScope.SubScope("update_status")
 	scope = SetGitScopeTags(scope, repo.FullName, pull.Num)
 
diff --git a/server/events/working_dir.go b/server/events/working_dir.go
index f77378a2a4..3d2d9fa2b9 100644
--- a/server/events/working_dir.go
+++ b/server/events/working_dir.go
@@ -79,9 +79,9 @@ type FileWorkspace struct {
 	// TestingOverrideBaseCloneURL can be used during testing to override the
 	// URL of the base repo to be cloned. If it's empty then we clone normally.
 	TestingOverrideBaseCloneURL string
-	// GithubAppEnabled is true if we should fetch the ref "pull/PR_NUMBER/head"
-	// from the "origin" remote. If this is false, we fetch "+refs/heads/$HEAD_BRANCH"
-	// from the "head" remote.
+	// GithubAppEnabled is true and a PR number is supplied, we should fetch
+	// the ref "pull/PR_NUMBER/head" from the "origin" remote. If this is false,
+	// we fetch "+refs/heads/$HEAD_BRANCH" from the "head" remote.
 	GithubAppEnabled bool
 	// use the global setting without overriding
 	GpgNoSigningEnabled bool
@@ -106,12 +106,13 @@ func (w *FileWorkspace) Clone(logger logging.SimpleLogging, headRepo models.Repo
 		logger.Debug("clone directory '%s' already exists, checking if it's at the right commit", cloneDir)
 
 		// We use git rev-parse to see if our repo is at the right commit.
-		// If just checking out the pull request branch, we can use HEAD.
+		// If just checking out the pull request branch or if there is no
+		// pull request (API triggered with a custom git ref), we can use HEAD.
 		// If doing a merge, then HEAD won't be at the pull request's HEAD
 		// because we'll already have performed a merge. Instead, we'll check
 		// HEAD^2 since that will be the commit before our merge.
 		pullHead := "HEAD"
-		if w.CheckoutMerge {
+		if w.CheckoutMerge && c.pr.Num > 0 {
 			pullHead = "HEAD^2"
 		}
 		revParseCmd := exec.Command("git", "rev-parse", pullHead) // #nosec
@@ -331,7 +332,7 @@ func (w *FileWorkspace) wrappedGit(logger logging.SimpleLogging, c wrappedGitCon
 func (w *FileWorkspace) mergeToBaseBranch(logger logging.SimpleLogging, c wrappedGitContext) error {
 	fetchRef := fmt.Sprintf("+refs/heads/%s:", c.pr.HeadBranch)
 	fetchRemote := "head"
-	if w.GithubAppEnabled {
+	if w.GithubAppEnabled && c.pr.Num > 0 {
 		fetchRef = fmt.Sprintf("pull/%d/head:", c.pr.Num)
 		fetchRemote = "origin"
 	}