diff --git a/lib/redmine/helpers/gantt.rb b/lib/redmine/helpers/gantt.rb
index 7aba9b7e2..31956bfae 100644
--- a/lib/redmine/helpers/gantt.rb
+++ b/lib/redmine/helpers/gantt.rb
@@ -615,13 +615,13 @@ module Redmine
         zoom ||= @zoom
         coords = {}
         if start_date && end_date && start_date <= self.date_to && end_date >= self.date_from
-          if start_date > self.date_from
+          if start_date >= self.date_from
             coords[:start] = start_date - self.date_from
             coords[:bar_start] = start_date - self.date_from
           else
             coords[:bar_start] = 0
           end
-          if end_date < self.date_to
+          if end_date <= self.date_to
             coords[:end] = end_date - self.date_from + 1
             coords[:bar_end] = end_date - self.date_from + 1
           else
diff --git a/test/unit/lib/redmine/helpers/gantt_test.rb b/test/unit/lib/redmine/helpers/gantt_test.rb
index 770ae4719..e4e8cc6a9 100644
--- a/test/unit/lib/redmine/helpers/gantt_test.rb
+++ b/test/unit/lib/redmine/helpers/gantt_test.rb
@@ -450,6 +450,9 @@ class Redmine::Helpers::GanttHelperTest < Redmine::HelperTest
     @output_buffer = @gantt.line(today - 7, today + 7, 30, true, 'line', :format => :html, :zoom => 4)
     assert_select "div.starting", 1
     assert_select 'div.starting[style*="left:28px"]', 1
+    # starting marker on the leftmost boundary of the gantt
+    @output_buffer = @gantt.line(gantt_start, today + 7, 30, true, 'line', :format => :html, :zoom => 4)
+    assert_select 'div.starting[style*="left:0px"]', 1
   end
 
   test "#line starting marker should not appear if the start date is before gantt start date" do
@@ -463,6 +466,9 @@ class Redmine::Helpers::GanttHelperTest < Redmine::HelperTest
     @output_buffer = @gantt.line(today - 7, today + 7, 30, true, 'line', :format => :html, :zoom => 4)
     assert_select "div.ending", 1
     assert_select 'div.ending[style*="left:88px"]', 1
+    # ending marker on the rightmost boundary of the gantt
+    @output_buffer = @gantt.line(today - 7, gantt_end, 30, true, 'line', :format => :html, :zoom => 4)
+    assert_select 'div.ending[style*="left:116px"]', 1
   end
 
   test "#line ending marker should not appear if the end date is before gantt start date" do