diff --git a/lib/kamal/configuration.rb b/lib/kamal/configuration.rb
index 64c74c63c..f7f2233c0 100644
--- a/lib/kamal/configuration.rb
+++ b/lib/kamal/configuration.rb
@@ -263,6 +263,10 @@ def ensure_required_keys_present
         end
       end
 
+      unless role_names.include?(primary_web_role)
+        raise ArgumentError, "The primary_web_role #{primary_web_role} isn't defined"
+      end
+
       unless traefik_role_names.include?(primary_web_role)
         raise ArgumentError, "Role #{primary_web_role} needs to have traefik enabled"
       end