diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index c4c09e53bb1..4c3f7722468 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -540,23 +540,31 @@ vac_estimate_reltuples(Relation relation, bool is_analyze,
  *
  *		We violate transaction semantics here by overwriting the rel's
  *		existing pg_class tuple with the new values.  This is reasonably
- *		safe since the new values are correct whether or not this transaction
- *		commits.  The reason for this is that if we updated these tuples in
- *		the usual way, vacuuming pg_class itself wouldn't work very well ---
- *		by the time we got done with a vacuum cycle, most of the tuples in
- *		pg_class would've been obsoleted.  Of course, this only works for
- *		fixed-size never-null columns, but these are.
- *
- *		Note another assumption: that two VACUUMs/ANALYZEs on a table can't
- *		run in parallel, nor can VACUUM/ANALYZE run in parallel with a
- *		schema alteration such as adding an index, rule, or trigger.  Otherwise
- *		our updates of relhasindex etc might overwrite uncommitted updates.
+ *		safe as long as we're sure that the new values are correct whether or
+ *		not this transaction commits.  The reason for doing this is that if
+ *		we updated these tuples in the usual way, vacuuming pg_class itself
+ *		wouldn't work very well --- by the time we got done with a vacuum
+ *		cycle, most of the tuples in pg_class would've been obsoleted.  Of
+ *		course, this only works for fixed-size not-null columns, but these are.
  *
  *		Another reason for doing it this way is that when we are in a lazy
- *		VACUUM and have PROC_IN_VACUUM set, we mustn't do any updates ---
- *		somebody vacuuming pg_class might think they could delete a tuple
+ *		VACUUM and have PROC_IN_VACUUM set, we mustn't do any regular updates.
+ *		Somebody vacuuming pg_class might think they could delete a tuple
  *		marked with xmin = our xid.
  *
+ *		In addition to fundamentally nontransactional statistics such as
+ *		relpages and relallvisible, we try to maintain certain lazily-updated
+ *		DDL flags such as relhasindex, by clearing them if no longer correct.
+ *		It's safe to do this in VACUUM, which can't run in parallel with
+ *		CREATE INDEX/RULE/TRIGGER and can't be part of a transaction block.
+ *		However, it's *not* safe to do it in an ANALYZE that's within a
+ *		transaction block, because for example the current transaction might
+ *		have dropped the last index; then we'd think relhasindex should be
+ *		cleared, but if the transaction later rolls back this would be wrong.
+ *		So we refrain from updating the DDL flags if we're inside a
+ *		transaction block.  This is OK since postponing the flag maintenance
+ *		is always allowable.
+ *
  *		This routine is shared by VACUUM and ANALYZE.
  */
 void
@@ -579,7 +587,7 @@ vac_update_relstats(Relation relation,
 			 relid);
 	pgcform = (Form_pg_class) GETSTRUCT(ctup);
 
-	/* Apply required updates, if any, to copied tuple */
+	/* Apply statistical updates, if any, to copied tuple */
 
 	dirty = false;
 	if (pgcform->relpages != (int32) num_pages)
@@ -592,41 +600,50 @@ vac_update_relstats(Relation relation,
 		pgcform->reltuples = (float4) num_tuples;
 		dirty = true;
 	}
-	if (pgcform->relhasindex != hasindex)
-	{
-		pgcform->relhasindex = hasindex;
-		dirty = true;
-	}
 
-	/*
-	 * If we have discovered that there are no indexes, then there's no
-	 * primary key either, nor any exclusion constraints.  This could be done
-	 * more thoroughly...
-	 */
-	if (!hasindex)
+	/* Apply DDL updates, but not inside a transaction block (see above) */
+
+	if (!IsTransactionBlock())
 	{
-		if (pgcform->relhaspkey)
+		/*
+		 * If we didn't find any indexes, reset relhasindex.
+		 */
+		if (pgcform->relhasindex && !hasindex)
 		{
-			pgcform->relhaspkey = false;
+			pgcform->relhasindex = false;
 			dirty = true;
 		}
-		if (pgcform->relhasexclusion && pgcform->relkind != RELKIND_INDEX)
+
+		/*
+		 * If we have discovered that there are no indexes, then there's no
+		 * primary key either, nor any exclusion constraints.  This could be
+		 * done more thoroughly...
+		 */
+		if (!hasindex)
 		{
-			pgcform->relhasexclusion = false;
+			if (pgcform->relhaspkey)
+			{
+				pgcform->relhaspkey = false;
+				dirty = true;
+			}
+			if (pgcform->relhasexclusion && pgcform->relkind != RELKIND_INDEX)
+			{
+				pgcform->relhasexclusion = false;
+				dirty = true;
+			}
+		}
+
+		/* We also clear relhasrules and relhastriggers if needed */
+		if (pgcform->relhasrules && relation->rd_rules == NULL)
+		{
+			pgcform->relhasrules = false;
+			dirty = true;
+		}
+		if (pgcform->relhastriggers && relation->trigdesc == NULL)
+		{
+			pgcform->relhastriggers = false;
 			dirty = true;
 		}
-	}
-
-	/* We also clear relhasrules and relhastriggers if needed */
-	if (pgcform->relhasrules && relation->rd_rules == NULL)
-	{
-		pgcform->relhasrules = false;
-		dirty = true;
-	}
-	if (pgcform->relhastriggers && relation->trigdesc == NULL)
-	{
-		pgcform->relhastriggers = false;
-		dirty = true;
 	}
 
 	/*
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index 0da5ec58b56..e793a293b2f 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -1544,6 +1544,24 @@ select non_strict(NULL);
  
 (1 row)
 
+-- check for rollback of ANALYZE corrupting table property flags (bug #11638)
+CREATE TABLE check_fk_presence_1 (id int PRIMARY KEY, t text);
+NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "check_fk_presence_1_pkey" for table "check_fk_presence_1"
+CREATE TABLE check_fk_presence_2 (id int REFERENCES check_fk_presence_1, t text);
+BEGIN;
+ALTER TABLE check_fk_presence_2 DROP CONSTRAINT check_fk_presence_2_id_fkey;
+ANALYZE check_fk_presence_2;
+ROLLBACK;
+\d check_fk_presence_2
+Table "public.check_fk_presence_2"
+ Column |  Type   | Modifiers 
+--------+---------+-----------
+ id     | integer | 
+ t      | text    | 
+Foreign-key constraints:
+    "check_fk_presence_2_id_fkey" FOREIGN KEY (id) REFERENCES check_fk_presence_1(id)
+
+DROP TABLE check_fk_presence_1, check_fk_presence_2;
 --
 -- alter object set schema
 --
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 0a41fd85dc6..9cb69bb0264 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -1124,6 +1124,16 @@ select non_strict(NULL);
 alter function non_strict(text) returns null on null input;
 select non_strict(NULL);
 
+-- check for rollback of ANALYZE corrupting table property flags (bug #11638)
+CREATE TABLE check_fk_presence_1 (id int PRIMARY KEY, t text);
+CREATE TABLE check_fk_presence_2 (id int REFERENCES check_fk_presence_1, t text);
+BEGIN;
+ALTER TABLE check_fk_presence_2 DROP CONSTRAINT check_fk_presence_2_id_fkey;
+ANALYZE check_fk_presence_2;
+ROLLBACK;
+\d check_fk_presence_2
+DROP TABLE check_fk_presence_1, check_fk_presence_2;
+
 --
 -- alter object set schema
 --