--- a/js/src/gc/Statistics.cpp
+++ b/js/src/gc/Statistics.cpp
@@ -353,17 +353,17 @@ Statistics::formatData(StatisticsSeriali
                 continue;
             }
 
             ss.beginObject(NULL);
             ss.extra("    ");
             ss.appendNumber("Slice", "%d", "", i);
             ss.appendDecimal("Pause", "", t(width));
             ss.extra(" (");
-            ss.appendDecimal("When", "ms", t(slices[i].end - slices[0].start));
+            ss.appendDecimal("When", "ms", t(slices[i].start - slices[0].start));
             ss.appendString("Reason", ExplainReason(slices[i].reason));
             if (slices[i].resetReason)
                 ss.appendString("Reset", slices[i].resetReason);
             ss.extra("): ");
             FormatPhaseTimes(ss, "Times", slices[i].phaseTimes);
             if (ss.isJSON())
                 FormatPhaseFaults(ss, "Page Faults", slices[i].phaseFaults);
             ss.endLine();