diff --git a/src/backend/access/spgist/spgutils.c b/src/backend/access/spgist/spgutils.c
index 03a9cd36e6..3235d215e1 100644
--- a/src/backend/access/spgist/spgutils.c
+++ b/src/backend/access/spgist/spgutils.c
@@ -25,6 +25,7 @@
 #include "catalog/pg_amop.h"
 #include "commands/vacuum.h"
 #include "nodes/nodeFuncs.h"
+#include "parser/parse_coerce.h"
 #include "storage/bufmgr.h"
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
@@ -218,9 +219,20 @@ spgGetCache(Relation index)
 		 * correctly, so believe leafType if it's given.)
 		 */
 		if (!OidIsValid(cache->config.leafType))
+		{
 			cache->config.leafType =
 				TupleDescAttr(RelationGetDescr(index), spgKeyColumn)->atttypid;
 
+			/*
+			 * If index column type is binary-coercible to atttype (for
+			 * example, it's a domain over atttype), treat it as plain atttype
+			 * to avoid thinking we need to compress.
+			 */
+			if (cache->config.leafType != atttype &&
+				IsBinaryCoercible(cache->config.leafType, atttype))
+				cache->config.leafType = atttype;
+		}
+
 		/* Get the information we need about each relevant datatype */
 		fillTypeDesc(&cache->attType, atttype);
 
diff --git a/src/test/regress/expected/spgist.out b/src/test/regress/expected/spgist.out
index 9364b88bc2..1688e0e0a3 100644
--- a/src/test/regress/expected/spgist.out
+++ b/src/test/regress/expected/spgist.out
@@ -65,3 +65,24 @@ DETAIL:  Valid values are between "10" and "100".
 -- Modify fillfactor in existing index
 alter index spgist_point_idx set (fillfactor = 90);
 reindex index spgist_point_idx;
+-- Test index over a domain
+create domain spgist_text as varchar;
+create table spgist_domain_tbl (f1 spgist_text);
+create index spgist_domain_idx on spgist_domain_tbl using spgist(f1);
+insert into spgist_domain_tbl values('fee'), ('fi'), ('fo'), ('fum');
+explain (costs off)
+select * from spgist_domain_tbl where f1 = 'fo';
+                  QUERY PLAN                   
+-----------------------------------------------
+ Bitmap Heap Scan on spgist_domain_tbl
+   Recheck Cond: ((f1)::text = 'fo'::text)
+   ->  Bitmap Index Scan on spgist_domain_idx
+         Index Cond: ((f1)::text = 'fo'::text)
+(4 rows)
+
+select * from spgist_domain_tbl where f1 = 'fo';
+ f1 
+----
+ fo
+(1 row)
+
diff --git a/src/test/regress/sql/spgist.sql b/src/test/regress/sql/spgist.sql
index c72cf42a33..7644f344a9 100644
--- a/src/test/regress/sql/spgist.sql
+++ b/src/test/regress/sql/spgist.sql
@@ -71,3 +71,12 @@ create index spgist_point_idx2 on spgist_point_tbl using spgist(p) with (fillfac
 -- Modify fillfactor in existing index
 alter index spgist_point_idx set (fillfactor = 90);
 reindex index spgist_point_idx;
+
+-- Test index over a domain
+create domain spgist_text as varchar;
+create table spgist_domain_tbl (f1 spgist_text);
+create index spgist_domain_idx on spgist_domain_tbl using spgist(f1);
+insert into spgist_domain_tbl values('fee'), ('fi'), ('fo'), ('fum');
+explain (costs off)
+select * from spgist_domain_tbl where f1 = 'fo';
+select * from spgist_domain_tbl where f1 = 'fo';