diff --git a/ppl/src/main/java/org/opensearch/sql/ppl/utils/PPLQueryDataAnonymizer.java b/ppl/src/main/java/org/opensearch/sql/ppl/utils/PPLQueryDataAnonymizer.java
index 3e7528ab27..a1ca0fd69a 100644
--- a/ppl/src/main/java/org/opensearch/sql/ppl/utils/PPLQueryDataAnonymizer.java
+++ b/ppl/src/main/java/org/opensearch/sql/ppl/utils/PPLQueryDataAnonymizer.java
@@ -247,7 +247,7 @@ public String visitFillNull(FillNull node, String context) {
           firstReplacement,
           node.getNullableFieldFills().stream()
               .map(n -> visitExpression(n.getNullableFieldReference()))
-              .collect(Collectors.joining(",")));
+              .collect(Collectors.joining(", ")));
     } else {
       return StringUtils.format(
           "%s | fillnull using %s",