diff --git a/moveit_ros/planning/planning_pipeline/res/planning_pipeline_parameters.yaml b/moveit_ros/planning/planning_pipeline/res/planning_pipeline_parameters.yaml
index 6b115762ea..f4b582e3ad 100644
--- a/moveit_ros/planning/planning_pipeline/res/planning_pipeline_parameters.yaml
+++ b/moveit_ros/planning/planning_pipeline/res/planning_pipeline_parameters.yaml
@@ -7,5 +7,5 @@ planning_pipeline_parameters:
   request_adapters: {
     type: string,
     description: "Names of the planning request adapter plugins (plugin names separated by space).",
-    default_value: "UNKNOWN",
+    default_value: "",
   }
diff --git a/moveit_ros/planning/planning_pipeline/src/planning_pipeline.cpp b/moveit_ros/planning/planning_pipeline/src/planning_pipeline.cpp
index 12b33c63ce..24f31c7cb6 100644
--- a/moveit_ros/planning/planning_pipeline/src/planning_pipeline.cpp
+++ b/moveit_ros/planning/planning_pipeline/src/planning_pipeline.cpp
@@ -107,11 +107,11 @@ void planning_pipeline::PlanningPipeline::configure()
     throw;
   }
 
-  if (planner_plugin_name_.empty())
+  if (planner_plugin_name_.empty() || planner_plugin_name_ == "UNKNOWN")
   {
     std::string classes_str = fmt::format("{}", fmt::join(planner_plugin_loader_->getDeclaredClasses(), ", "));
-    throw std::runtime_error("Planning plugin name is empty. Please choose one of the available plugins: " +
-                             classes_str);
+    throw std::runtime_error("Planning plugin name is empty or not defined in namespace '" + parameter_namespace_ +
+                             "'. Please choose one of the available plugins: " + classes_str);
   }
 
   try