diff --git a/public/app/plugins/datasource/prometheus/datasource.ts b/public/app/plugins/datasource/prometheus/datasource.ts
index 122fe9601a1..0782170fbd9 100644
--- a/public/app/plugins/datasource/prometheus/datasource.ts
+++ b/public/app/plugins/datasource/prometheus/datasource.ts
@@ -173,6 +173,9 @@ export class PrometheusDatasource {
       throw { message: 'Invalid time range' };
     }
 
+    start = start - (start % query.step);
+    end = end - (end % query.step) + query.step;
+
     var url =
       '/api/v1/query_range?query=' +
       encodeURIComponent(query.expr) +