diff --git a/app/services/weights_and_measures.rb b/app/services/weights_and_measures.rb
index 78846e6e859..170dacb2088 100644
--- a/app/services/weights_and_measures.rb
+++ b/app/services/weights_and_measures.rb
@@ -15,9 +15,11 @@ def scale_for_unit_value
 
   def system
     return "custom" unless scales = scales_for_variant_unit(ignore_available_units: true)
-    return "custom" unless product_scale = @variant.product.variant_unit_scale
 
-    scales[product_scale.to_f]['system']
+    product_scale = @variant.product.variant_unit_scale&.to_f
+    return "custom" unless product_scale.present? && product_scale.positive?
+
+    scales[product_scale]['system']
   end
 
   # @returns enumerable with label and value for select
diff --git a/spec/services/weights_and_measures_spec.rb b/spec/services/weights_and_measures_spec.rb
index 3f6d742b339..0992316886c 100644
--- a/spec/services/weights_and_measures_spec.rb
+++ b/spec/services/weights_and_measures_spec.rb
@@ -91,7 +91,7 @@
         expect(subject.system).to eq("custom")
       end
 
-      pending "when unit is valid, but scale is 0" do
+      it "when unit is valid, but scale is 0" do
         allow(product).to receive(:variant_unit) { "weight" }
         allow(product).to receive(:variant_unit_scale) { 0.0 }
         expect(subject.system).to eq("custom")