diff --git a/app/models/issue.rb b/app/models/issue.rb
index ab9f794db..2b488c0fd 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -1838,19 +1838,20 @@ class Issue < ActiveRecord::Base
           if children.any?
             child_with_total_estimated_hours = children.select {|c| c.total_estimated_hours.to_f > 0.0}
             if child_with_total_estimated_hours.any?
-              average =
-                child_with_total_estimated_hours.sum(&:total_estimated_hours).to_d /
-                  child_with_total_estimated_hours.count
+              average = Rational(
+                child_with_total_estimated_hours.sum(&:total_estimated_hours).to_d,
+                child_with_total_estimated_hours.count
+              )
             else
-              average = BigDecimal('1.0')
+              average = Rational(1)
             end
             done = children.sum do |c|
-              estimated = (c.total_estimated_hours || 0.0).to_d
+              estimated = Rational(c.total_estimated_hours&.to_d || 0)
               estimated = average unless estimated > 0.0
               ratio = c.closed? ? 100 : (c.done_ratio || 0)
               estimated * ratio
             end
-            progress = done / (average * children.count)
+            progress = Rational(done, average * children.count)
             p.done_ratio = progress.floor
           end
         end