diff --git a/slack-strava/models/map.rb b/slack-strava/models/map.rb
index 2d6d697..b0175c7 100644
--- a/slack-strava/models/map.rb
+++ b/slack-strava/models/map.rb
@@ -53,7 +53,10 @@ def png_size
   end
 
   def to_s
-    "proxy=#{proxy_image_url}, png=#{png_size} byte(s)"
+    [
+      "proxy=#{proxy_image_url}",
+      png ? "png=#{png_size} byte(s)" : nil
+    ].compact.join(', ')
   end
 
   def delete_png!
diff --git a/spec/models/map_spec.rb b/spec/models/map_spec.rb
new file mode 100644
index 0000000..60b3b8c
--- /dev/null
+++ b/spec/models/map_spec.rb
@@ -0,0 +1,24 @@
+require 'spec_helper'
+
+describe Map do
+  let(:activity) { Fabricate(:user_activity) }
+  let(:map) { activity.map }
+
+  context 'to_s' do
+    context 'without png' do
+      it 'includes proxy URL' do
+        expect(map.to_s).to eq "proxy=https://slava.playplay.io/api/maps/#{map.id}.png"
+      end
+    end
+
+    context 'with png' do
+      before do
+        map.png = BSON::Binary.new(SecureRandom.hex)
+      end
+
+      it 'includes proxy URL' do
+        expect(map.to_s).to eq "proxy=https://slava.playplay.io/api/maps/#{map.id}.png, png=32 byte(s)"
+      end
+    end
+  end
+end