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-rw-r--r--io_buffer.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/io_buffer.c b/io_buffer.c
index 2e789abe0f..cc76f12ecc 100644
--- a/io_buffer.c
+++ b/io_buffer.c
@@ -843,7 +843,8 @@ rb_io_buffer_get_bytes(VALUE self, void **base, size_t *size)
static inline void
io_buffer_get_bytes_for_writing(struct rb_io_buffer *buffer, void **base, size_t *size)
{
- if (buffer->flags & RB_IO_BUFFER_READONLY) {
+ if (buffer->flags & RB_IO_BUFFER_READONLY ||
+ (!NIL_P(buffer->source) && OBJ_FROZEN(buffer->source))) {
rb_raise(rb_eIOBufferAccessError, "Buffer is not writable!");
}