diff --git a/internal/handlers/handlers.go b/internal/handlers/handlers.go
index 1134c72..8fe1d1c 100644
--- a/internal/handlers/handlers.go
+++ b/internal/handlers/handlers.go
@@ -56,6 +56,7 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("GET /pulls/{owner}/{repo}/{index}", h.PullDetail)
 	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/review", h.SubmitReview)
 	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/state", h.SetPullState)
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
 
 	// Settings (handled separately for auth bypass).
 	settingsHandler := &SettingsHandler{
diff --git a/internal/handlers/integration_test.go b/internal/handlers/integration_test.go
index b5dcd3e..f8c4dbc 100644
--- a/internal/handlers/integration_test.go
+++ b/internal/handlers/integration_test.go
@@ -726,6 +726,66 @@ func TestIntegration_AssignIssue_MissingAssignee(t *testing.T) {
 	}
 }
 
+// --- Issue #228: Integration tests for POST /pulls/{owner}/{repo}/{index}/assignees ---
+
+func TestIntegration_AssignPull_Valid(t *testing.T) {
+	h, srv := newTestHandlerWithMock(t)
+	defer srv.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
+
+	form := url.Values{"assignee": {"user1"}}
+	req := reqWithToken(http.MethodPost, "/pulls/test-org/repo1/1/assignees", form.Encode())
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusSeeOther {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusSeeOther)
+	}
+}
+
+func TestIntegration_AssignPull_HTMX(t *testing.T) {
+	h, srv := newTestHandlerWithMock(t)
+	defer srv.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
+
+	form := url.Values{"assignee": {"user1"}}
+	req := reqWithToken(http.MethodPost, "/pulls/test-org/repo1/1/assignees", form.Encode())
+	req.Header.Set("HX-Request", "true")
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusOK)
+	}
+	body := w.Body.String()
+	if !contains(body, "Assigned to user1") {
+		t.Errorf("expected 'Assigned to user1' in HTMX response, got: %s", body)
+	}
+}
+
+func TestIntegration_AssignPull_MissingAssignee(t *testing.T) {
+	h, srv := newTestHandlerWithMock(t)
+	defer srv.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
+
+	req := reqWithToken(http.MethodPost, "/pulls/test-org/repo1/1/assignees", "")
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusBadRequest)
+	}
+}
+
 // --- Issue #118: Integration tests for CloseIssue and AddComment ---
 
 func TestIntegration_CloseIssue(t *testing.T) {