diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 716de171a4..3d5adab2c5 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -2559,7 +2559,7 @@ CompareIndexInfo(const IndexInfo *info1, const IndexInfo *info2,
 
 	/*
 	 * and columns match through the attribute map (actual attribute numbers
-	 * might differ!)  Note that this implies that index columns that are
+	 * might differ!)  Note that this checks that index columns that are
 	 * expressions appear in the same positions.  We will next compare the
 	 * expressions themselves.
 	 */
@@ -2568,13 +2568,22 @@ CompareIndexInfo(const IndexInfo *info1, const IndexInfo *info2,
 		if (attmap->maplen < info2->ii_IndexAttrNumbers[i])
 			elog(ERROR, "incorrect attribute map");
 
-		/* ignore expressions at this stage */
-		if ((info1->ii_IndexAttrNumbers[i] != InvalidAttrNumber) &&
-			(attmap->attnums[info2->ii_IndexAttrNumbers[i] - 1] !=
-			 info1->ii_IndexAttrNumbers[i]))
-			return false;
+		/* ignore expressions for now (but check their collation/opfamily) */
+		if (!(info1->ii_IndexAttrNumbers[i] == InvalidAttrNumber &&
+			  info2->ii_IndexAttrNumbers[i] == InvalidAttrNumber))
+		{
+			/* fail if just one index has an expression in this column */
+			if (info1->ii_IndexAttrNumbers[i] == InvalidAttrNumber ||
+				info2->ii_IndexAttrNumbers[i] == InvalidAttrNumber)
+				return false;
+
+			/* both are columns, so check for match after mapping */
+			if (attmap->attnums[info2->ii_IndexAttrNumbers[i] - 1] !=
+				info1->ii_IndexAttrNumbers[i])
+				return false;
+		}
 
-		/* collation and opfamily is not valid for including columns */
+		/* collation and opfamily are not valid for included columns */
 		if (i >= info1->ii_NumIndexKeyAttrs)
 			continue;