diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index c477314efa..bbe67ed8bb 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -722,6 +722,45 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 				break;
 		}
 
+		/*
+		 * Check that relation is a legal target for marking.
+		 *
+		 * In most cases parser and/or planner should have noticed this
+		 * already, but they don't cover all cases.
+		 */
+		if (relation)
+		{
+			switch (relation->rd_rel->relkind)
+			{
+				case RELKIND_RELATION:
+					/* OK */
+					break;
+				case RELKIND_SEQUENCE:
+					/* Must disallow this because we don't vacuum sequences */
+					ereport(ERROR,
+							(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+							 errmsg("cannot lock rows in sequence \"%s\"",
+									RelationGetRelationName(relation))));
+					break;
+				case RELKIND_TOASTVALUE:
+					/* This will be disallowed in 9.1, but for now OK */
+					break;
+				case RELKIND_VIEW:
+					/* Should not get here */
+					ereport(ERROR,
+							(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+							 errmsg("cannot lock rows in view \"%s\"",
+									RelationGetRelationName(relation))));
+					break;
+				default:
+					ereport(ERROR,
+							(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+							 errmsg("cannot lock rows in relation \"%s\"",
+									RelationGetRelationName(relation))));
+					break;
+			}
+		}
+
 		erm = (ExecRowMark *) palloc(sizeof(ExecRowMark));
 		erm->relation = relation;
 		erm->rti = rc->rti;