diff --git a/lib/cooked_post_processor.rb b/lib/cooked_post_processor.rb
index e58f17bd1..02686aaf1 100644
--- a/lib/cooked_post_processor.rb
+++ b/lib/cooked_post_processor.rb
@@ -98,7 +98,10 @@ class CookedPostProcessor
     return unless image_sizes.present?
     image_sizes.each do |image_size|
       url, size = image_size[0], image_size[1]
-      return [size["width"], size["height"]] if url && size && url.include?(src)
+      if url && url.include?(src) &&
+         size && size["width"].to_i > 0 && size["height"].to_i > 0
+        return [size["width"], size["height"]]
+      end
     end
   end
 
diff --git a/spec/components/cooked_post_processor_spec.rb b/spec/components/cooked_post_processor_spec.rb
index 6b5ff79f4..02d50f82f 100644
--- a/spec/components/cooked_post_processor_spec.rb
+++ b/spec/components/cooked_post_processor_spec.rb
@@ -40,20 +40,48 @@ describe CookedPostProcessor do
 
   context ".post_process_images" do
 
-    context "with image_sizes" do
-
-      let(:post) { build(:post_with_image_urls) }
-      let(:cpp) { CookedPostProcessor.new(post, image_sizes: {"http://foo.bar/image.png" => {"width" => 111, "height" => 222}}) }
-
-      before { cpp.post_process_images }
-
-      it "works" do
+    shared_examples "leave dimensions alone" do
+      it "doesn't use them" do
         # adds the width from the image sizes provided when no dimension is provided
-        expect(cpp.html).to match(/src="http:\/\/foo.bar\/image.png" width="111" height="222"/)
+        expect(cpp.html).to match(/src="http:\/\/foo.bar\/image.png" width="" height=""/)
         # adds the width from the image sizes provided
         expect(cpp.html).to match(/src="http:\/\/domain.com\/picture.jpg" width="50" height="42"/)
         expect(cpp).to be_dirty
       end
+    end
+
+    context "with image_sizes" do
+      let(:post) { build(:post_with_image_urls) }
+      let(:cpp) { CookedPostProcessor.new(post, image_sizes: image_sizes) }
+
+      before { cpp.post_process_images }
+
+      context "valid" do
+        let(:image_sizes) { {"http://foo.bar/image.png" => {"width" => 111, "height" => 222}} }
+
+        it "use them" do
+          # adds the width from the image sizes provided when no dimension is provided
+          expect(cpp.html).to match(/src="http:\/\/foo.bar\/image.png" width="111" height="222"/)
+          # adds the width from the image sizes provided
+          expect(cpp.html).to match(/src="http:\/\/domain.com\/picture.jpg" width="50" height="42"/)
+          expect(cpp).to be_dirty
+        end
+      end
+
+      context "invalid width" do
+        let(:image_sizes) { {"http://foo.bar/image.png" => {"width" => 0, "height" => 222}} }
+        include_examples "leave dimensions alone"
+      end
+
+      context "invalid height" do
+        let(:image_sizes) { {"http://foo.bar/image.png" => {"width" => 111, "height" => 0}} }
+        include_examples "leave dimensions alone"
+      end
+
+      context "invalid width & height" do
+        let(:image_sizes) { {"http://foo.bar/image.png" => {"width" => 0, "height" => 0}} }
+        include_examples "leave dimensions alone"
+      end
 
     end