diff --git a/src/libFLAC/metadata_iterators.c b/src/libFLAC/metadata_iterators.c
index 4527878..4fd58c8 100644
--- a/src/libFLAC/metadata_iterators.c
+++ b/src/libFLAC/metadata_iterators.c
@@ -837,6 +837,11 @@ FLAC_API FLAC__bool FLAC__metadata_simple_iterator_delete_block(FLAC__Metadata_S
 	FLAC__ASSERT_DECLARATION(FLAC__off_t debug_target_offset = iterator->offset[iterator->depth];)
 	FLAC__bool ret;
 
+	if(!iterator->is_writable) {
+		iterator->status = FLAC__METADATA_SIMPLE_ITERATOR_STATUS_NOT_WRITABLE;
+		return false;
+	}
+
 	if(iterator->type == FLAC__METADATA_TYPE_STREAMINFO) {
 		iterator->status = FLAC__METADATA_SIMPLE_ITERATOR_STATUS_ILLEGAL_INPUT;
 		return false;