diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index d04cf4bccf8..6019d9b03ff 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -2661,18 +2661,21 @@ simplify_permutation (gimple_stmt_iterator *gsi)
 
       /* Shuffle of a constructor.  */
       bool ret = false;
-      tree res_type = TREE_TYPE (gimple_assign_lhs (stmt));
+      tree res_type = TREE_TYPE (arg0);
       tree opt = fold_ternary (VEC_PERM_EXPR, res_type, arg0, arg1, op2);
       if (!opt
 	  || (TREE_CODE (opt) != CONSTRUCTOR && TREE_CODE (opt) != VECTOR_CST))
 	return 0;
       /* Found VIEW_CONVERT_EXPR before, need one explicit conversion.  */
-      if (res_type != TREE_TYPE (op0))
+      tree lhs_type = TREE_TYPE (gimple_assign_lhs (stmt));
+      if (res_type != lhs_type)
 	{
+	  if (!operand_equal_p (TYPE_SIZE (lhs_type), TYPE_SIZE (res_type)))
+	    return 0;
 	  tree name = make_ssa_name (TREE_TYPE (opt));
 	  gimple *ass_stmt = gimple_build_assign (name, opt);
 	  gsi_insert_before (gsi, ass_stmt, GSI_SAME_STMT);
-	  opt = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (op0), name);
+	  opt = build1 (VIEW_CONVERT_EXPR, lhs_type, name);
 	}
       gimple_assign_set_rhs_from_tree (gsi, opt);
       update_stmt (gsi_stmt (*gsi));