diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index c601b6d40d..3aa3d8a7f5 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -451,11 +451,13 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 	qry->hasWindowFuncs = pstate->p_hasWindowFuncs;
 	qry->hasTargetSRFs = pstate->p_hasTargetSRFs;
 	qry->hasAggs = pstate->p_hasAggs;
-	if (pstate->p_hasAggs)
-		parseCheckAggregates(pstate, qry);
 
 	assign_query_collations(pstate, qry);
 
+	/* this must be done after collations, for reliable comparison of exprs */
+	if (pstate->p_hasAggs)
+		parseCheckAggregates(pstate, qry);
+
 	return qry;
 }
 
@@ -1318,8 +1320,6 @@ transformSelectStmt(ParseState *pstate, SelectStmt *stmt)
 	qry->hasWindowFuncs = pstate->p_hasWindowFuncs;
 	qry->hasTargetSRFs = pstate->p_hasTargetSRFs;
 	qry->hasAggs = pstate->p_hasAggs;
-	if (pstate->p_hasAggs || qry->groupClause || qry->groupingSets || qry->havingQual)
-		parseCheckAggregates(pstate, qry);
 
 	foreach(l, stmt->lockingClause)
 	{
@@ -1329,6 +1329,10 @@ transformSelectStmt(ParseState *pstate, SelectStmt *stmt)
 
 	assign_query_collations(pstate, qry);
 
+	/* this must be done after collations, for reliable comparison of exprs */
+	if (pstate->p_hasAggs || qry->groupClause || qry->groupingSets || qry->havingQual)
+		parseCheckAggregates(pstate, qry);
+
 	return qry;
 }
 
@@ -1790,8 +1794,6 @@ transformSetOperationStmt(ParseState *pstate, SelectStmt *stmt)
 	qry->hasWindowFuncs = pstate->p_hasWindowFuncs;
 	qry->hasTargetSRFs = pstate->p_hasTargetSRFs;
 	qry->hasAggs = pstate->p_hasAggs;
-	if (pstate->p_hasAggs || qry->groupClause || qry->groupingSets || qry->havingQual)
-		parseCheckAggregates(pstate, qry);
 
 	foreach(l, lockingClause)
 	{
@@ -1801,6 +1803,10 @@ transformSetOperationStmt(ParseState *pstate, SelectStmt *stmt)
 
 	assign_query_collations(pstate, qry);
 
+	/* this must be done after collations, for reliable comparison of exprs */
+	if (pstate->p_hasAggs || qry->groupClause || qry->groupingSets || qry->havingQual)
+		parseCheckAggregates(pstate, qry);
+
 	return qry;
 }
 
diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index a21bf1dc6b..deed5bef46 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -2116,3 +2116,22 @@ SELECT min(x ORDER BY y) FROM (VALUES(1, 2)) AS d(x,y);
    1
 (1 row)
 
+-- check collation-sensitive matching between grouping expressions
+select v||'a', case v||'a' when 'aa' then 1 else 0 end, count(*)
+  from unnest(array['a','b']) u(v)
+ group by v||'a' order by 1;
+ ?column? | case | count 
+----------+------+-------
+ aa       |    1 |     1
+ ba       |    0 |     1
+(2 rows)
+
+select v||'a', case when v||'a' = 'aa' then 1 else 0 end, count(*)
+  from unnest(array['a','b']) u(v)
+ group by v||'a' order by 1;
+ ?column? | case | count 
+----------+------+-------
+ aa       |    1 |     1
+ ba       |    0 |     1
+(2 rows)
+
diff --git a/src/test/regress/expected/groupingsets.out b/src/test/regress/expected/groupingsets.out
index c7deec2ff4..381ebce8a1 100644
--- a/src/test/regress/expected/groupingsets.out
+++ b/src/test/regress/expected/groupingsets.out
@@ -1540,4 +1540,29 @@ explain (costs off)
          ->  Seq Scan on tenk1
 (12 rows)
 
+-- check collation-sensitive matching between grouping expressions
+-- (similar to a check for aggregates, but there are additional code
+-- paths for GROUPING, so check again here)
+select v||'a', case grouping(v||'a') when 1 then 1 else 0 end, count(*)
+  from unnest(array[1,1], array['a','b']) u(i,v)
+ group by rollup(i, v||'a') order by 1,3;
+ ?column? | case | count 
+----------+------+-------
+ aa       |    0 |     1
+ ba       |    0 |     1
+          |    1 |     2
+          |    1 |     2
+(4 rows)
+
+select v||'a', case when grouping(v||'a') = 1 then 1 else 0 end, count(*)
+  from unnest(array[1,1], array['a','b']) u(i,v)
+ group by rollup(i, v||'a') order by 1,3;
+ ?column? | case | count 
+----------+------+-------
+ aa       |    0 |     1
+ ba       |    0 |     1
+          |    1 |     2
+          |    1 |     2
+(4 rows)
+
 -- end
diff --git a/src/test/regress/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index b2d8583e09..a03f897bcc 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -935,3 +935,11 @@ SELECT dense_rank(x) WITHIN GROUP (ORDER BY x) FROM (VALUES (1),(1),(2),(2),(3),
 -- 2a505161-2727-2473-7c46-591ed108ac52@email.cz
 SELECT min(x ORDER BY y) FROM (VALUES(1, NULL)) AS d(x,y);
 SELECT min(x ORDER BY y) FROM (VALUES(1, 2)) AS d(x,y);
+
+-- check collation-sensitive matching between grouping expressions
+select v||'a', case v||'a' when 'aa' then 1 else 0 end, count(*)
+  from unnest(array['a','b']) u(v)
+ group by v||'a' order by 1;
+select v||'a', case when v||'a' = 'aa' then 1 else 0 end, count(*)
+  from unnest(array['a','b']) u(v)
+ group by v||'a' order by 1;
diff --git a/src/test/regress/sql/groupingsets.sql b/src/test/regress/sql/groupingsets.sql
index c32d23b8d7..5d6485913b 100644
--- a/src/test/regress/sql/groupingsets.sql
+++ b/src/test/regress/sql/groupingsets.sql
@@ -415,4 +415,15 @@ explain (costs off)
          count(*)
     from tenk1 group by grouping sets (unique1,twothousand,thousand,hundred,ten,four,two);
 
+-- check collation-sensitive matching between grouping expressions
+-- (similar to a check for aggregates, but there are additional code
+-- paths for GROUPING, so check again here)
+
+select v||'a', case grouping(v||'a') when 1 then 1 else 0 end, count(*)
+  from unnest(array[1,1], array['a','b']) u(i,v)
+ group by rollup(i, v||'a') order by 1,3;
+select v||'a', case when grouping(v||'a') = 1 then 1 else 0 end, count(*)
+  from unnest(array[1,1], array['a','b']) u(i,v)
+ group by rollup(i, v||'a') order by 1,3;
+
 -- end