diff --git a/frontend/lib/chart-utils.ts b/frontend/lib/chart-utils.ts
index aa863c03..5da70d96 100644
--- a/frontend/lib/chart-utils.ts
+++ b/frontend/lib/chart-utils.ts
@@ -411,6 +411,17 @@ export function getTemperatureChartData(
       ? Number((temp + offset).toFixed(1))
       : null,
   );
+  const firstValid = debTemps.findIndex((t) => t != null);
+  const lastValid = (() => {
+    for (let i = debTemps.length - 1; i >= 0; i--) {
+      if (debTemps[i] != null) return i;
+    }
+    return -1;
+  })();
+  if (firstValid >= 0 && lastValid >= 0) {
+    for (let i = 0; i < firstValid; i++) debTemps[i] = debTemps[firstValid];
+    for (let i = lastValid + 1; i < debTemps.length; i++) debTemps[i] = debTemps[lastValid];
+  }
   const debPast = debTemps.map((temp, index) =>
     currentIndex >= 0 && index <= currentIndex ? temp : null,
   );