diff --git a/app/controllers/api/base_controller.rb b/app/controllers/api/base_controller.rb
index 0980e0ebbc..b10c2f5737 100644
--- a/app/controllers/api/base_controller.rb
+++ b/app/controllers/api/base_controller.rb
@@ -72,6 +72,13 @@ class Api::BaseController < ApplicationController
     end
   end
 
+  # Redefine `require_functional!` to properly output JSON instead of HTML redirects
+  def require_functional!
+    return if current_user.functional?
+
+    require_user!
+  end
+
   def render_empty
     render json: {}, status: 200
   end
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 62e3355ae6..081b435811 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -71,7 +71,23 @@ class ApplicationController < ActionController::Base
   end
 
   def require_functional!
-    redirect_to edit_user_registration_path unless current_user.functional?
+    return if current_user.functional?
+
+    respond_to do |format|
+      format.any do
+        redirect_to edit_user_registration_path
+      end
+
+      format.json do
+        if !current_user.confirmed?
+          render json: { error: 'Your login is missing a confirmed e-mail address' }, status: 403
+        elsif !current_user.approved?
+          render json: { error: 'Your login is currently pending approval' }, status: 403
+        elsif !current_user.functional?
+          render json: { error: 'Your login is currently disabled' }, status: 403
+        end
+      end
+    end
   end
 
   def skip_csrf_meta_tags?