diff --git a/src/components/dashboard/activity-calendar.tsx b/src/components/dashboard/activity-calendar.tsx
index 0e06259..059e1de 100644
--- a/src/components/dashboard/activity-calendar.tsx
+++ b/src/components/dashboard/activity-calendar.tsx
@@ -93,6 +93,12 @@ export function ActivityCalendar({
           {grid.weeks.map((week, weekIndex) =>
             week.map((day, dayIndex) => {
               if (!day.inRange) return null;
+              // Single template-literal child: React 19's HTML serializer drops
+              // mixed text/expression children inside <title> elements when
+              // emitted as SSR markup, causing a hydration mismatch where the
+              // client re-adds the text. One pre-formatted string keeps the
+              // server and client output identical.
+              const tooltipText = `${day.date}: ${day.count} ${day.count === 1 ? "commit" : "commits"}`;
               return (
                 <rect
                   key={day.date}
@@ -103,10 +109,7 @@ export function ActivityCalendar({
                   rx={2}
                   fill={fill(day.level)}
                 >
-                  <title>
-                    {day.date}: {day.count}{" "}
-                    {day.count === 1 ? "commit" : "commits"}
-                  </title>
+                  <title>{tooltipText}</title>
                 </rect>
               );
             })