diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index cf1c123b72..502b103685 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -418,11 +418,13 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 	qry->hasSubLinks = pstate->p_hasSubLinks;
 	qry->hasWindowFuncs = pstate->p_hasWindowFuncs;
 	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;
 }
 
@@ -1255,8 +1257,6 @@ transformSelectStmt(ParseState *pstate, SelectStmt *stmt)
 	qry->hasSubLinks = pstate->p_hasSubLinks;
 	qry->hasWindowFuncs = pstate->p_hasWindowFuncs;
 	qry->hasAggs = pstate->p_hasAggs;
-	if (pstate->p_hasAggs || qry->groupClause || qry->groupingSets || qry->havingQual)
-		parseCheckAggregates(pstate, qry);
 
 	foreach(l, stmt->lockingClause)
 	{
@@ -1266,6 +1266,10 @@ 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;
 }
 
@@ -1715,8 +1719,6 @@ transformSetOperationStmt(ParseState *pstate, SelectStmt *stmt)
 	qry->hasSubLinks = pstate->p_hasSubLinks;
 	qry->hasWindowFuncs = pstate->p_hasWindowFuncs;
 	qry->hasAggs = pstate->p_hasAggs;
-	if (pstate->p_hasAggs || qry->groupClause || qry->groupingSets || qry->havingQual)
-		parseCheckAggregates(pstate, qry);
 
 	foreach(l, lockingClause)
 	{
@@ -1726,6 +1728,10 @@ 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 e768b1fe6d..a1663f08c2 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -2047,3 +2047,22 @@ SELECT balk(hundred) FROM tenk1;
 (1 row)
 
 ROLLBACK;
+-- 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 976050c2d0..44fe5afcdc 100644
--- a/src/test/regress/expected/groupingsets.out
+++ b/src/test/regress/expected/groupingsets.out
@@ -921,4 +921,29 @@ select sum(ten) from onek group by rollup(four::text), two order by 1;
  2500
 (6 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 cb28f4cffe..7e129f74bc 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -900,3 +900,11 @@ EXPLAIN (COSTS OFF) SELECT balk(hundred) FROM tenk1;
 SELECT balk(hundred) FROM tenk1;
 
 ROLLBACK;
+
+-- 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 77cdb5acba..85830e92d2 100644
--- a/src/test/regress/sql/groupingsets.sql
+++ b/src/test/regress/sql/groupingsets.sql
@@ -255,4 +255,15 @@ select array(select row(v.a,s1.*) from (select two,four, count(*) from onek grou
 select sum(ten) from onek group by two, rollup(four::text) order by 1;
 select sum(ten) from onek group by rollup(four::text), two order by 1;
 
+-- 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