diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 09dc9ccb5ec..5c56658a271 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1616,6 +1616,7 @@ _outIndexOptInfo(StringInfo str, IndexOptInfo *node)
 	WRITE_NODE_FIELD(indpred);
 	WRITE_BOOL_FIELD(predOK);
 	WRITE_BOOL_FIELD(unique);
+	WRITE_BOOL_FIELD(immediate);
 	WRITE_BOOL_FIELD(hypothetical);
 }
 
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 2c97bea3fa3..e43e12d8832 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -1948,10 +1948,11 @@ relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel,
 		int			c;
 
 		/*
-		 * If the index is not unique or if it's a partial index that doesn't
-		 * match the query, it's useless here.
+		 * If the index is not unique, or not immediately enforced, or if it's
+		 * a partial index that doesn't match the query, it's useless here.
 		 */
-		if (!ind->unique || (ind->indpred != NIL && !ind->predOK))
+		if (!ind->unique || !ind->immediate ||
+			(ind->indpred != NIL && !ind->predOK))
 			continue;
 
 		/*
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index e35c8c326d7..f7fb38404f2 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -275,6 +275,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 				ChangeVarNodes((Node *) info->indpred, 1, varno, 0);
 			info->predOK = false;		/* set later in indxpath.c */
 			info->unique = index->indisunique;
+			info->immediate = index->indimmediate;
 			info->hypothetical = false;
 
 			/*
@@ -876,6 +877,11 @@ join_selectivity(PlannerInfo *root,
  * Detect whether there is a unique index on the specified attribute
  * of the specified relation, thus allowing us to conclude that all
  * the (non-null) values of the attribute are distinct.
+ *
+ * This function does not check the index's indimmediate property, which
+ * means that uniqueness may transiently fail to hold intra-transaction.
+ * That's appropriate when we are making statistical estimates, but beware
+ * of using this for any correctness proofs.
  */
 bool
 has_unique_index(RelOptInfo *rel, AttrNumber attno)
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 7c1567a2cc3..6989627adc3 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -4102,7 +4102,9 @@ get_join_variables(PlannerInfo *root, List *args, SpecialJoinInfo *sjinfo,
  *		commonly the same as the exposed type of the variable argument,
  *		but can be different in binary-compatible-type cases.
  *	isunique: TRUE if we were able to match the var to a unique index,
- *		implying its values are unique for this query.
+ *		implying its values are unique for this query.  (Caution: this
+ *		should be trusted for statistical purposes only, since we do not
+ *		check indimmediate.)
  *
  * Caller is responsible for doing ReleaseVariableStats() before exiting.
  */
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 7d39e10747a..dc3a37eae95 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -473,6 +473,8 @@ typedef struct IndexOptInfo
 	bool		amhasgetbitmap; /* does AM have amgetbitmap interface? */
 	/* added in 9.0.4: */
 	bool		hypothetical;	/* true if index doesn't really exist */
+	/* added in 9.0.6: */
+	bool		immediate;		/* is uniqueness enforced immediately? */
 } IndexOptInfo;