diff --git a/api.go b/api.go
index 50ca187..0bbdb7f 100644
--- a/api.go
+++ b/api.go
@@ -47,7 +47,10 @@ type MarkdownRequest struct {
 
 // repos gets a list of Git repositories in this organisation.
 func (this *Application) repos(ctx context.Context) ([]Repo, error) {
-	this.apiSem.Acquire(ctx, 1)
+	err := this.apiSem.Acquire(ctx, 1)
+	if err != nil {
+		return nil, err // e.g. ctx closed
+	}
 	defer this.apiSem.Release(1)
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, this.cfg.Gitea.URL+`api/v1/orgs/`+url.PathEscape(this.cfg.Gitea.Org)+`/repos`, nil)
@@ -77,7 +80,10 @@ func (this *Application) repos(ctx context.Context) ([]Repo, error) {
 // repoFile gets a single file from the default branch of the git repository
 // Usually the default branch is `master`.
 func (this *Application) repoFile(ctx context.Context, repo, filename string) ([]byte, error) {
-	this.apiSem.Acquire(ctx, 1)
+	err := this.apiSem.Acquire(ctx, 1)
+	if err != nil {
+		return nil, err // e.g. ctx closed
+	}
 	defer this.apiSem.Release(1)
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, this.cfg.Gitea.URL+`api/v1/repos/`+url.PathEscape(this.cfg.Gitea.Org)+`/`+url.PathEscape(repo)+`/contents/`+url.PathEscape(filename), nil)
@@ -105,7 +111,10 @@ func (this *Application) repoFile(ctx context.Context, repo, filename string) ([
 }
 
 func (this *Application) filesInDirectory(ctx context.Context, repo, dir string) ([]ReaddirEntry, error) {
-	this.apiSem.Acquire(ctx, 1)
+	err := this.apiSem.Acquire(ctx, 1)
+	if err != nil {
+		return nil, err // e.g. ctx closed
+	}
 	defer this.apiSem.Release(1)
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, this.cfg.Gitea.URL+`api/v1/repos/`+url.PathEscape(this.cfg.Gitea.Org)+`/`+url.PathEscape(repo)+`/contents/`+dir, nil) // n.b. $dir param not escaped
@@ -168,7 +177,10 @@ func (this *Application) imageFilesForRepo(ctx context.Context, repo string) ([]
 }
 
 func (this *Application) topicsForRepo(ctx context.Context, repo string) ([]string, error) {
-	this.apiSem.Acquire(ctx, 1)
+	err := this.apiSem.Acquire(ctx, 1)
+	if err != nil {
+		return nil, err // e.g. ctx closed
+	}
 	defer this.apiSem.Release(1)
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, this.cfg.Gitea.URL+`api/v1/repos/`+url.PathEscape(this.cfg.Gitea.Org)+`/`+url.PathEscape(repo)+`/topics`, nil)
@@ -197,7 +209,10 @@ func (this *Application) topicsForRepo(ctx context.Context, repo string) ([]stri
 
 // renderMarkdown calls the remote Gitea server's own markdown renderer.
 func (this *Application) renderMarkdown(ctx context.Context, repoName string, body string) ([]byte, error) {
-	this.apiSem.Acquire(ctx, 1)
+	err := this.apiSem.Acquire(ctx, 1)
+	if err != nil {
+		return nil, err // e.g. ctx closed
+	}
 	defer this.apiSem.Release(1)
 
 	jb, err := json.Marshal(MarkdownRequest{
@@ -231,7 +246,10 @@ func (this *Application) renderMarkdown(ctx context.Context, repoName string, bo
 
 // renderMarkdownRaw calls the remote Gitea server's own markdown renderer.
 func (this *Application) renderMarkdownRaw(ctx context.Context, body []byte) ([]byte, error) {
-	this.apiSem.Acquire(ctx, 1)
+	err := this.apiSem.Acquire(ctx, 1)
+	if err != nil {
+		return nil, err // e.g. ctx closed
+	}
 	defer this.apiSem.Release(1)
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, this.cfg.Gitea.URL+`api/v1/markdown/raw`, bytes.NewReader(body))