diff --git a/lib/uh/wm/manager.rb b/lib/uh/wm/manager.rb
index 1abd171..cd3a723 100644
--- a/lib/uh/wm/manager.rb
+++ b/lib/uh/wm/manager.rb
@@ -6,6 +6,7 @@ module Uh
                     Events::SUBSTRUCTURE_REDIRECT_MASK |
                     Events::SUBSTRUCTURE_NOTIFY_MASK |
                     Events::STRUCTURE_NOTIFY_MASK
+      DEFAULT_GEO = Geo.new(0, 0, 320, 240).freeze
 
       attr_reader :modifier, :display, :clients
 
@@ -45,6 +46,15 @@ module Uh
         @display.grab_key keysym.to_s, mod_mask
       end
 
+      def configure window
+        if client = client_for(window)
+          client.configure
+        else
+          geo = @events.emit :configure, args: window
+          window.configure_event geo ? geo : DEFAULT_GEO
+        end
+      end
+
       def manage window
         return if window.override_redirect? || client_for(window)
         @clients << client = Client.new(window)
diff --git a/spec/uh/wm/manager_spec.rb b/spec/uh/wm/manager_spec.rb
index 63d3e81..e15638c 100644
--- a/spec/uh/wm/manager_spec.rb
+++ b/spec/uh/wm/manager_spec.rb
@@ -2,6 +2,7 @@ module Uh
   module WM
     RSpec.describe Manager do
       let(:block)       { proc { } }
+      let(:window)      { instance_spy Window, override_redirect?: false }
       let(:events)      { Dispatcher.new }
       let(:modifier)    { :mod1 }
       let(:display)     { Display.new }
@@ -106,9 +107,35 @@ module Uh
         end
       end
 
-      describe '#manage' do
-        let(:window) { instance_spy Window, override_redirect?: false }
+      describe '#configure' do
+        context 'with new window' do
+          it 'sends a configure event to the window with a default geo' do
+            expect(window)
+              .to receive(:configure_event).with(Geo.new(0, 0, 320, 240))
+            manager.configure window
+          end
 
+          context 'when :configure event returns a geo' do
+            it 'sends a configure event with geo returned by event' do
+              geo = Geo.new(0, 0, 42, 42)
+              events.on(:configure) { geo }
+              expect(window).to receive(:configure_event).with geo
+              manager.configure window
+            end
+          end
+        end
+
+        context 'with known window' do
+          before { manager.manage window }
+
+          it 'tells the client to configure' do
+            expect(manager.clients[0]).to receive :configure
+            manager.configure window
+          end
+        end
+      end
+
+      describe '#manage' do
         it 'registers a new client wrapping the given window' do
           manager.manage window
           expect(manager.clients[0])