diff --git a/spec/diagram_spec.rb b/spec/diagram_spec.rb
index 32733fefb..4e1f508e4 100644
--- a/spec/diagram_spec.rb
+++ b/spec/diagram_spec.rb
@@ -41,7 +41,8 @@
     (expect Pathname.new output_file 'images/pdfwidth-test.png').to exist
     images = pdf.images
     (expect images).to have_size 1
-    (expect images[0][:intrinsic_width].to_f).to eql 288.0
+    image_data = JSON.load_file Pathname.new output_file '.asciidoctor/diagram/pdfwidth-test.png.cache'
+    (expect images[0][:intrinsic_width].to_f).to eql image_data['width'].to_f
     (expect images[0][:width].to_f).to eql 72.0
   end