diff --git a/lib/redmine/i18n.rb b/lib/redmine/i18n.rb
index a9cd1dd0d..6d893ad22 100644
--- a/lib/redmine/i18n.rb
+++ b/lib/redmine/i18n.rb
@@ -94,8 +94,9 @@ module Redmine
 
       minutes = (hours * 60).round
       if Setting.timespan_format == 'minutes'
-        h, m = minutes.divmod(60)
-        "%d:%02d" % [h, m]
+        h, m = minutes.abs.divmod(60)
+        sign = minutes.negative? ? '-' : ''
+        "%s%d:%02d" % [sign, h, m]
       else
         number_with_delimiter(sprintf('%.2f', minutes.fdiv(60)), delimiter: nil)
       end
diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index 573eda42b..f959744e2 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -2210,11 +2210,15 @@ class ApplicationHelperTest < Redmine::HelperTest
     set_language_if_valid 'en'
 
     with_settings :timespan_format => 'minutes' do
+      assert_equal '-0:45', format_hours(-0.75)
+      assert_equal '0:00', format_hours(0)
       assert_equal '0:45', format_hours(0.75)
       assert_equal '0:45 h', l_hours_short(0.75)
       assert_equal '0:45 hour', l_hours(0.75)
     end
     with_settings :timespan_format => 'decimal' do
+      assert_equal '-0.75', format_hours(-0.75)
+      assert_equal '0.00', format_hours(0)
       assert_equal '0.75', format_hours(0.75)
       assert_equal '0.75 h', l_hours_short(0.75)
       assert_equal '0.75 hour', l_hours(0.75)