diff --git a/modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/matrix/stats/MatrixStatsAggregatorFactory.java b/modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/matrix/stats/MatrixStatsAggregatorFactory.java
index bb3771bfd5762..55d930128d0f6 100644
--- a/modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/matrix/stats/MatrixStatsAggregatorFactory.java
+++ b/modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/matrix/stats/MatrixStatsAggregatorFactory.java
@@ -55,7 +55,7 @@ protected Aggregator doCreateInternal(
         for (Map.Entry<String, ValuesSource> entry : valuesSources.entrySet()) {
             if (entry.getValue() instanceof ValuesSource.Numeric == false) {
                 throw new AggregationExecutionException(
-                    "ValuesSource type " + entry.getValue().toString() + "is not supported for aggregation " + this.name()
+                    "ValuesSource type [" + entry.getValue().toString() + "] is not supported for aggregation [" + this.name() + "]"
                 );
             }
             // TODO: There must be a better option than this.