diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index a3b2300408a..e18e23409c8 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -391,11 +391,13 @@ 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;
 }
 
@@ -1010,8 +1012,6 @@ 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->havingQual)
-		parseCheckAggregates(pstate, qry);
 
 	foreach(l, stmt->lockingClause)
 	{
@@ -1021,6 +1021,10 @@ 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->havingQual)
+		parseCheckAggregates(pstate, qry);
+
 	return qry;
 }
 
@@ -1470,8 +1474,6 @@ 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->havingQual)
-		parseCheckAggregates(pstate, qry);
 
 	foreach(l, lockingClause)
 	{
@@ -1481,6 +1483,10 @@ 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->havingQual)
+		parseCheckAggregates(pstate, qry);
+
 	return qry;
 }
 
diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index a43f674a9e3..887df315f04 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -1655,3 +1655,22 @@ select least_agg(variadic array[q1,q2]) from int8_tbl;
  -4567890123456789
 (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/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index c12a2d8b7b6..a6310dd18f5 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -612,3 +612,11 @@ drop view aggordview1;
 -- variadic aggregates
 select least_agg(q1,q2) from int8_tbl;
 select least_agg(variadic array[q1,q2]) from int8_tbl;
+
+-- 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;