--- a/libskk/file-dict.c
+++ b/libskk/file-dict.c
@@ -336,7 +336,7 @@ skk_file_dict_read_until (SkkFileDict* s
 	_tmp0_ = self->priv->mmap;
 	_tmp1_ = skk_memory_mapped_file_get_length (_tmp0_);
 	_tmp2_ = _tmp1_;
-	g_return_val_if_fail (((gsize) (*offset)) < _tmp2_, NULL);
+	g_return_val_if_fail (((gsize) (*offset)) < _tmp2_, FALSE);
 	while (TRUE) {
 		gint _tmp3_;
 		gint _tmp4_;
