diff --git a/server/cache.go b/server/cache.go
index bb0c3d1..8bc4246 100644
--- a/server/cache.go
+++ b/server/cache.go
@@ -16,7 +16,7 @@ type stat struct {
 	Summary      check.Result `json:"summary"`
 }
 
-var dayAggregation map[string]map[time.Time]stat
+var dayAggregation = make(map[string]map[time.Time]stat)
 
 func convertToResult(successCount, totalCount int) check.Result {
 	if successCount >= totalCount*99/100 {
@@ -29,6 +29,9 @@ func convertToResult(successCount, totalCount int) check.Result {
 }
 
 func getDay(serviceName string, day time.Time) stat {
+	if _, ok := dayAggregation[serviceName]; !ok {
+		dayAggregation[serviceName] = make(map[time.Time]stat)
+	}
 	if cached, ok := dayAggregation[serviceName][day]; ok {
 		return cached
 	}