diff --git a/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java b/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java
index ddd91b1bed8..07c0470b937 100644
--- a/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java
+++ b/core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java
@@ -448,7 +448,7 @@ public AggregateCall rename(@Nullable String name) {
       }
       buf.append(")");
     }
-    if (!collation.equals(RelCollations.EMPTY)) {
+    if (hasCollation()) {
       buf.append(" WITHIN GROUP (");
       buf.append(collation);
       buf.append(")");
@@ -465,6 +465,11 @@ public boolean hasFilter() {
     return filterArg >= 0;
   }
 
+  /** Returns true if this AggregateCall has a non-empty collation. Returns false otherwise. */
+  public boolean hasCollation() {
+    return !collation.equals(RelCollations.EMPTY);
+  }
+
   /** Withs {@link #filterArg}. */
   public AggregateCall withFilter(int filterArg) {
     return filterArg == this.filterArg ? this
diff --git a/core/src/main/java/org/apache/calcite/rel/rules/AggregateExpandWithinDistinctRule.java b/core/src/main/java/org/apache/calcite/rel/rules/AggregateExpandWithinDistinctRule.java
index a47a68ca93f..111cf0c6b6f 100644
--- a/core/src/main/java/org/apache/calcite/rel/rules/AggregateExpandWithinDistinctRule.java
+++ b/core/src/main/java/org/apache/calcite/rel/rules/AggregateExpandWithinDistinctRule.java
@@ -348,10 +348,13 @@ int getCount(int filterArg) {
       if (c.distinctKeys == null) {
         RelBuilder.AggCall aggCall =
             b.aggregateCall(c.getParserPosition(), c.getAggregation(), b.fields(c.getArgList()));
-        registrar.registerAgg(i,
-            c.hasFilter()
-                ? aggCall.filter(b.field(c.filterArg))
-                : aggCall);
+        if (c.hasFilter()) {
+          aggCall = aggCall.filter(b.field(c.filterArg));
+        }
+        if (c.hasCollation()) {
+          aggCall = aggCall.sort(b.fields(c.getCollation()));
+        }
+        registrar.registerAgg(i, aggCall);
       } else {
         for (int inputIdx : c.getArgList()) {
           registrar.register(inputIdx, c.filterArg);
diff --git a/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java b/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java
index cb15194c038..859e5422574 100644
--- a/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java
+++ b/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java
@@ -2417,6 +2417,24 @@ private void checkSemiOrAntiJoinProjectTranspose(JoinRelType type) {
     sql(sql).withProgram(program).check();
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-6595">[CALCITE-6595]
+   * Preserve collation for non-distinct aggregate calls with AggregateExpandWithinDistinctRule</a>.
+   *
+   * <p>Tests {@link AggregateExpandWithinDistinctRule} with a non-distinct aggregate with a WITHIN
+   * GROUP (ORDER BY) clause that includes a distinct aggregate in the same query. */
+  @Test void testWithinDistinctPreservesNonDistinctCollation() {
+    final String sql = "SELECT SUM(sal) WITHIN DISTINCT (job),\n"
+  + "LISTAGG(ename, '; ') WITHIN GROUP (ORDER BY sal DESC)\n"
+  + "  FROM Emp\n"
+  + "GROUP BY deptno";
+    HepProgram program = new HepProgramBuilder()
+        .addRuleInstance(CoreRules.AGGREGATE_REDUCE_FUNCTIONS)
+        .addRuleInstance(CoreRules.AGGREGATE_EXPAND_WITHIN_DISTINCT)
+        .build();
+    sql(sql).withProgram(program).check();
+  }
+
   /** Tests {@link AggregateExpandWithinDistinctRule}. Includes multiple
    * different filters for the aggregate calls, and all aggregate calls have the
    * same distinct keys, so there is no need to filter based on
diff --git a/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml b/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml
index ec4d69b9c08..84f9305bf51 100644
--- a/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml
+++ b/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml
@@ -17378,6 +17378,33 @@ LogicalProject(DEPTNO=[$0], EXPR$1=[CASE(=($2, 0), null:INTEGER, $1)], EXPR$2=[$
         LogicalAggregate(group=[{0, 3}], groups=[[{0, 3}, {0}]], agg#0=[$SUM0($1) FILTER $2], agg#1=[COUNT() FILTER $2], agg#2=[MIN($1)], agg#3=[MAX($1)], agg#4=[GROUPING($0, $3)])
           LogicalProject(DEPTNO=[$7], SAL=[$5], $f2=[>($5, 1000)], JOB=[$2])
             LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+]]>
+    </Resource>
+  </TestCase>
+  <TestCase name="testWithinDistinctPreservesNonDistinctCollation">
+    <Resource name="sql">
+      <![CDATA[SELECT SUM(sal) WITHIN DISTINCT (job),
+LISTAGG(ename, '; ') WITHIN GROUP (ORDER BY sal DESC)
+  FROM Emp
+GROUP BY deptno]]>
+    </Resource>
+    <Resource name="planBefore">
+      <![CDATA[
+LogicalProject(EXPR$0=[$1], EXPR$1=[$2])
+  LogicalAggregate(group=[{0}], EXPR$0=[SUM($1) WITHIN DISTINCT ($2)], EXPR$1=[LISTAGG($3, $4) WITHIN GROUP ([1 DESC])])
+    LogicalProject(DEPTNO=[$7], SAL=[$5], JOB=[$2], ENAME=[$1], $f4=['; '])
+      LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+]]>
+    </Resource>
+    <Resource name="planAfter">
+      <![CDATA[
+LogicalProject(EXPR$0=[$1], EXPR$1=[$2])
+  LogicalProject(DEPTNO=[$0], $f1=[$1], $f2=[CAST($2):VARCHAR(20) NOT NULL])
+    LogicalAggregate(group=[{0}], agg#0=[$SUM0($1) FILTER $3], agg#1=[MIN($2) FILTER $4])
+      LogicalProject(DEPTNO=[$0], $f2=[$2], $f4=[$4], $f6=[AND(=($5, 0), $THROW_UNLESS(OR(<>($5, 0), =($2, $3)), 'more than one distinct value in agg UNIQUE_VALUE'))], $f7=[=($5, 1)])
+        LogicalAggregate(group=[{0, 2}], groups=[[{0, 2}, {0}]], agg#0=[MIN($1)], agg#1=[MAX($1)], agg#2=[LISTAGG($3, $4) WITHIN GROUP ([1 DESC])], agg#3=[GROUPING($0, $2)])
+          LogicalProject(DEPTNO=[$7], SAL=[$5], JOB=[$2], ENAME=[$1], $f4=['; '])
+            LogicalTableScan(table=[[CATALOG, SALES, EMP]])
 ]]>
     </Resource>
   </TestCase>