diff --git a/src/commands/CmdChart.cpp b/src/commands/CmdChart.cpp
index ae616a5e..4f3c85cf 100644
--- a/src/commands/CmdChart.cpp
+++ b/src/commands/CmdChart.cpp
@@ -45,7 +45,7 @@ static std::string renderDayName         (const std::string&, const Rules&, Date
 static std::string renderTotal           (const std::string&, const Rules&, time_t);
 static std::string renderSubTotal        (const std::string&, const Rules&, int, int, time_t);
 static void        renderExclusionBlocks (const std::string&, const Rules&, std::vector <Composite>&, Palette&, const Datetime&, int, int, const std::vector <Range>&);
-static void        renderInterval        (const std::string&, const Rules&, std::vector <Composite>&, const Datetime&, const Interval&, Palette&, std::map <std::string, Color>&, time_t&);
+static void        renderInterval        (const std::string&, const Rules&, std::vector <Composite>&, const Datetime&, const Interval&, Palette&, std::map <std::string, Color>&, int, time_t&);
        std::string renderHolidays        (const std::string&, const Rules&, const Interval&);
 static std::string renderSummary         (const std::string&, const Rules&, const std::string&, const Interval&, const std::vector <Range>&, const std::vector <Interval>&, bool);
 
@@ -174,7 +174,7 @@ int renderChart (
       for (auto& track : tracked)
       {
         time_t interval_work = 0;
-        renderInterval (type, rules, lines, day, track, palette, tag_colors, interval_work);
+        renderInterval (type, rules, lines, day, track, palette, tag_colors, first_hour, interval_work);
         work += interval_work;
       }
     }
@@ -208,6 +208,8 @@ int renderChart (
 }
 
 ////////////////////////////////////////////////////////////////////////////////
+// Scan all tracked intervals, looking for the earliest and latest hour into
+// which an interval extends.
 static void determineHourRange (
   const std::string& type,
   const Rules& rules,
@@ -217,6 +219,7 @@ static void determineHourRange (
 {
   if (rules.get ("reports." + type + ".hours") == "auto")
   {
+    // Default to the full day.
     first_hour = 0;
     last_hour = 23;
 
@@ -443,6 +446,7 @@ static void renderInterval (
   const Interval& track,
   Palette& palette,
   std::map <std::string, Color>& tag_colors,
+  int first_hour,
   time_t& work)
 {
   auto spacing = rules.getInteger ("reports." + type + ".spacing");
@@ -457,8 +461,8 @@ static void renderInterval (
   if (track.range.is_open ())
     clipped.range.end = Datetime ();
 
-  auto start_mins = clipped.range.start.hour () * 60 + clipped.range.start.minute ();
-  auto end_mins   = clipped.range.end.hour () * 60 + clipped.range.end.minute ();
+  auto start_mins = (clipped.range.start.hour () - first_hour) * 60 + clipped.range.start.minute ();
+  auto end_mins   = (clipped.range.end.hour ()   - first_hour) * 60 + clipped.range.end.minute ();
   if (end_mins == 0)
     end_mins = (23 * 60) + 59;