diff --git a/lib/open_feature/sdk/configuration.rb b/lib/open_feature/sdk/configuration.rb
index 10591459..b1df9d6d 100644
--- a/lib/open_feature/sdk/configuration.rb
+++ b/lib/open_feature/sdk/configuration.rb
@@ -235,8 +235,7 @@ def run_immediate_handler(event_type, handler, client)
             provider_state = @provider_state_registry.get_state(provider)
 
             if event_type == status_to_event[provider_state]
-              provider_name = extract_provider_name(provider)
-              event_details = {provider_name: provider_name}
+              event_details = build_event_details(provider)
 
               begin
                 handler.call(event_details)
@@ -253,8 +252,7 @@ def run_immediate_handler(event_type, handler, client)
           provider_state = @provider_state_registry.get_state(client_provider)
 
           if event_type == status_to_event[provider_state]
-            provider_name = extract_provider_name(client_provider)
-            event_details = {provider_name: provider_name}
+            event_details = build_event_details(client_provider)
 
             begin
               handler.call(event_details)
@@ -264,6 +262,11 @@ def run_immediate_handler(event_type, handler, client)
           end
         end
       end
+
+      def build_event_details(provider)
+        stored_details = @provider_state_registry.get_details(provider)
+        {provider_name: extract_provider_name(provider)}.merge(stored_details)
+      end
     end
   end
 end
diff --git a/lib/open_feature/sdk/provider_state_registry.rb b/lib/open_feature/sdk/provider_state_registry.rb
index c4b5940c..b825b2cf 100644
--- a/lib/open_feature/sdk/provider_state_registry.rb
+++ b/lib/open_feature/sdk/provider_state_registry.rb
@@ -17,7 +17,7 @@ def set_initial_state(provider, state = ProviderState::NOT_READY)
         return unless provider
 
         @mutex.synchronize do
-          @states[provider.object_id] = state
+          @states[provider.object_id] = {state: state, details: {}}
         end
       end
 
@@ -29,7 +29,7 @@ def update_state_from_event(provider, event_type, event_details = nil)
         # Only update state if the event should cause a state change
         if new_state
           @mutex.synchronize do
-            @states[provider.object_id] = new_state
+            @states[provider.object_id] = {state: new_state, details: event_details || {}}
           end
           new_state
         else
@@ -42,7 +42,17 @@ def get_state(provider)
         return ProviderState::NOT_READY unless provider
 
         @mutex.synchronize do
-          @states[provider.object_id] || ProviderState::NOT_READY
+          entry = @states[provider.object_id]
+          entry ? entry[:state] : ProviderState::NOT_READY
+        end
+      end
+
+      def get_details(provider)
+        return {} unless provider
+
+        @mutex.synchronize do
+          entry = @states[provider.object_id]
+          entry ? entry[:details] : {}
         end
       end
 
diff --git a/spec/specification/events_spec.rb b/spec/specification/events_spec.rb
index bce81f5e..588f2faa 100644
--- a/spec/specification/events_spec.rb
+++ b/spec/specification/events_spec.rb
@@ -98,6 +98,66 @@ def init(_evaluation_context)
     end
   end
 
+  context "Requirement 5.1.4" do
+    specify "PROVIDER_ERROR events SHOULD populate the error message field" do
+      event_details_received = nil
+      handler = ->(event_details) { event_details_received = event_details }
+
+      OpenFeature::SDK.add_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_ERROR, handler)
+
+      provider = OpenFeature::SDK::Provider::InMemoryProvider.new
+      allow(provider).to receive(:init).and_raise("Custom init failure")
+
+      OpenFeature::SDK.set_provider(provider)
+      sleep(0.001) until event_details_received
+
+      expect(event_details_received[:message]).to eq("Custom init failure")
+
+      OpenFeature::SDK.remove_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_ERROR, handler)
+    end
+  end
+
+  context "Requirement 5.1.5" do
+    specify "PROVIDER_ERROR events SHOULD populate the error code field" do
+      event_details_received = nil
+      handler = ->(event_details) { event_details_received = event_details }
+
+      OpenFeature::SDK.add_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_ERROR, handler)
+
+      provider = OpenFeature::SDK::Provider::InMemoryProvider.new
+      allow(provider).to receive(:init).and_raise("Init failed")
+
+      OpenFeature::SDK.set_provider(provider)
+      sleep(0.001) until event_details_received
+
+      expect(event_details_received[:error_code]).to eq(OpenFeature::SDK::Provider::ErrorCode::GENERAL)
+
+      OpenFeature::SDK.remove_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_ERROR, handler)
+    end
+
+    specify "error details are available in immediate handlers attached after the error" do
+      provider = OpenFeature::SDK::Provider::InMemoryProvider.new
+      allow(provider).to receive(:init).and_raise("Delayed failure")
+
+      begin
+        OpenFeature::SDK.set_provider_and_wait(provider)
+      rescue OpenFeature::SDK::ProviderInitializationError
+        # Expected — provider init fails, putting provider in ERROR state
+      end
+
+      event_details_received = nil
+      handler = ->(event_details) { event_details_received = event_details }
+
+      OpenFeature::SDK.add_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_ERROR, handler)
+
+      expect(event_details_received).not_to be_nil
+      expect(event_details_received[:error_code]).to eq(OpenFeature::SDK::Provider::ErrorCode::GENERAL)
+      expect(event_details_received[:message]).to eq("Delayed failure")
+
+      OpenFeature::SDK.remove_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_ERROR, handler)
+    end
+  end
+
   context "Requirement 5.2.1" do
     specify "The client MUST provide a function for associating handler functions with provider event types" do
       client = OpenFeature::SDK.build_client(domain: "test-domain")