Merge PR #10742

public/app/plugins/panel/heatmap/heatmap_tooltip.ts

@@ -153,8 +153,12 @@ export class HeatmapTooltip {
 
   getXBucketIndex(offsetX, data) {
     let x = this.scope.xScale.invert(offsetX - this.scope.yAxisWidth).valueOf();
-    let xBucketIndex = getValueBucketBound(x, data.xBucketSize, 1);
-    return xBucketIndex;
+    // First try to find X bucket by checking x pos is in the
+    // [bucket.x, bucket.x + xBucketSize] interval
+    let xBucket = _.find(data.buckets, bucket => {
+      return x > bucket.x && x - bucket.x <= data.xBucketSize;
+    });
+    return xBucket ? xBucket.x : getValueBucketBound(x, data.xBucketSize, 1);
   }
 
   getYBucketIndex(offsetY, data) {