diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
index eaa28f0b7ed..7e5fc2cfdd8 100644
--- a/contrib/pg_upgrade/check.c
+++ b/contrib/pg_upgrade/check.c
@@ -17,6 +17,7 @@ static void check_locale_and_encoding(migratorContext *ctx, ControlData *oldctrl
 static void check_for_isn_and_int8_passing_mismatch(migratorContext *ctx,
 												Cluster whichCluster);
 static void check_for_reg_data_type_usage(migratorContext *ctx, Cluster whichCluster);
+static void check_for_invalid_indexes(migratorContext *ctx, Cluster whichCluster);
 
 
 /*
@@ -96,6 +97,7 @@ check_old_cluster(migratorContext *ctx, bool live_check,
 
 	check_for_reg_data_type_usage(ctx, CLUSTER_OLD);
 	check_for_isn_and_int8_passing_mismatch(ctx, CLUSTER_OLD);
+	check_for_invalid_indexes(ctx, CLUSTER_OLD);
 
 	/* old = PG 8.3 checks? */
 	if (GET_MAJOR_VERSION(ctx->old.major_version) <= 803)
@@ -676,3 +678,93 @@ check_for_reg_data_type_usage(migratorContext *ctx, Cluster whichCluster)
 	else
 		check_ok(ctx);
 }
+
+
+/*
+ * check_for_invalid_indexes()
+ *
+ *	CREATE INDEX CONCURRENTLY can create invalid indexes if the index build
+ *	fails.  These are dumped as valid indexes by pg_dump, but the
+ *	underlying files are still invalid indexes.  This checks to make sure
+ *	no invalid indexes exist, either failed index builds or concurrent
+ *	indexes in the process of being created.
+ */
+static void
+check_for_invalid_indexes(migratorContext *ctx, Cluster whichCluster)
+{
+	ClusterInfo *cluster = (whichCluster == CLUSTER_OLD) ?
+	&ctx->old : &ctx->new;
+	int			dbnum;
+	FILE	   *script = NULL;
+	bool		found = false;
+	char		output_path[MAXPGPATH];
+
+	prep_status(ctx, "Checking for invalid indexes from concurrent index builds");
+
+	snprintf(output_path, sizeof(output_path), "invalid_indexes.txt");
+
+	for (dbnum = 0; dbnum < cluster->dbarr.ndbs; dbnum++)
+	{
+		PGresult   *res;
+		bool		db_used = false;
+		int			ntups;
+		int			rowno;
+		int			i_nspname,
+					i_relname;
+		DbInfo	   *active_db = &cluster->dbarr.dbs[dbnum];
+		PGconn	   *conn = connectToServer(ctx, active_db->db_name, whichCluster);
+
+		res = executeQueryOrDie(ctx, conn,
+								"SELECT n.nspname, c.relname "
+								"FROM	pg_catalog.pg_class c, "
+								"		pg_catalog.pg_namespace n, "
+								"		pg_catalog.pg_index i "
+								"WHERE	(i.indisvalid = false OR "
+								"		 i.indisready = false) AND "
+								"		i.indexrelid = c.oid AND "
+								"		c.relnamespace = n.oid AND "
+								/* we do not migrate these, so skip them */
+							    " 		n.nspname != 'pg_catalog' AND "
+								"		n.nspname != 'information_schema' AND "
+								/* indexes do not have toast tables */
+								"		n.nspname != 'pg_toast'");
+
+		ntups = PQntuples(res);
+		i_nspname = PQfnumber(res, "nspname");
+		i_relname = PQfnumber(res, "relname");
+		for (rowno = 0; rowno < ntups; rowno++)
+		{
+			found = true;
+			if (script == NULL && (script = fopen(output_path, "w")) == NULL)
+				pg_log(ctx, PG_FATAL, "Could not create necessary file:  %s\n", output_path);
+			if (!db_used)
+			{
+				fprintf(script, "Database: %s\n", active_db->db_name);
+				db_used = true;
+			}
+			fprintf(script, "  %s.%s\n",
+					PQgetvalue(res, rowno, i_nspname),
+					PQgetvalue(res, rowno, i_relname));
+		}
+
+		PQclear(res);
+
+		PQfinish(conn);
+	}
+
+	if (script)
+		fclose(script);
+
+	if (found)
+	{
+		pg_log(ctx, PG_REPORT, "fatal\n");
+		pg_log(ctx, PG_FATAL,
+			   "Your installation contains invalid indexes due to failed or\n"
+		 	   "currently running CREATE INDEX CONCURRENTLY operations.  You\n"
+			   "cannot upgrade until these indexes are valid or removed.  A\n"
+			   "list of the problem indexes is in the file:\n"
+			   "    %s\n\n", output_path);
+	}
+	else
+		check_ok(ctx);
+}