diff --git a/sql/src/main/java/org/apache/druid/sql/calcite/aggregation/builtin/StringSqlAggregator.java b/sql/src/main/java/org/apache/druid/sql/calcite/aggregation/builtin/StringSqlAggregator.java
index af7b713317a7..b391100ff3a1 100644
--- a/sql/src/main/java/org/apache/druid/sql/calcite/aggregation/builtin/StringSqlAggregator.java
+++ b/sql/src/main/java/org/apache/druid/sql/calcite/aggregation/builtin/StringSqlAggregator.java
@@ -25,6 +25,7 @@
 import org.apache.calcite.rel.type.RelDataType;
 import org.apache.calcite.rex.RexBuilder;
 import org.apache.calcite.rex.RexLiteral;
+import org.apache.calcite.rex.RexNode;
 import org.apache.calcite.sql.SqlAggFunction;
 import org.apache.calcite.sql.SqlCallBinding;
 import org.apache.calcite.sql.SqlFunctionCategory;
@@ -109,36 +110,40 @@ public Aggregation toDruidAggregation(
       return null;
     }
 
+    RexNode separatorNode = Expressions.fromFieldAccess(
+        rexBuilder.getTypeFactory(),
+        rowSignature,
+        project,
+        aggregateCall.getArgList().get(1)
+    );
+    if (!separatorNode.isA(SqlKind.LITERAL)) {
+      // separator must be a literal
+      return null;
+    }
+
     final String separator;
 
-    if (arguments.size() > 1) {
-      separator = RexLiteral.stringValue(
-          Expressions.fromFieldAccess(
-              rexBuilder.getTypeFactory(),
-              rowSignature,
-              project,
-              aggregateCall.getArgList().get(1)
-          )
-      );
-    } else {
-      separator = "";
+    separator = RexLiteral.stringValue(separatorNode);
+
+    if (separator == null) {
+      // separator must not be null
+      return null;
     }
 
-    final HumanReadableBytes maxSizeBytes;
+    Integer maxSizeBytes = null;
 
     if (arguments.size() > 2) {
-      maxSizeBytes = HumanReadableBytes.valueOf(
-          RexLiteral.intValue(
-              Expressions.fromFieldAccess(
-                  rexBuilder.getTypeFactory(),
-                  rowSignature,
-                  project,
-                  aggregateCall.getArgList().get(2)
-              )
-          )
+      RexNode maxBytes = Expressions.fromFieldAccess(
+          rexBuilder.getTypeFactory(),
+          rowSignature,
+          project,
+          aggregateCall.getArgList().get(2)
       );
-    } else {
-      maxSizeBytes = null;
+      if (!maxBytes.isA(SqlKind.LITERAL)) {
+        // maxBytes must be a literal
+        return null;
+      }
+      maxSizeBytes = ((Number) RexLiteral.value(maxBytes)).intValue();
     }
 
     final DruidExpression arg = arguments.get(0);
@@ -176,7 +181,7 @@ public Aggregation toDruidAggregation(
                   StringUtils.format("array_set_add_all(\"__acc\", \"%s\")", name),
                   null,
                   finalizer,
-                  maxSizeBytes != null ? new HumanReadableBytes(maxSizeBytes.getBytes()) : null,
+                  maxSizeBytes != null ? new HumanReadableBytes(maxSizeBytes) : null,
                   macroTable
               ),
               dimFilter
@@ -199,7 +204,7 @@ public Aggregation toDruidAggregation(
                   StringUtils.format("array_concat(\"__acc\", \"%s\")", name),
                   null,
                   finalizer,
-                  maxSizeBytes != null ? new HumanReadableBytes(maxSizeBytes.getBytes()) : null,
+                  maxSizeBytes != null ? new HumanReadableBytes(maxSizeBytes) : null,
                   macroTable
               ),
               dimFilter