diff --git a/libvips/iofuncs/sinkdisc.c b/libvips/iofuncs/sinkdisc.c
index f686d6fc..3abd0bb9 100644
--- a/libvips/iofuncs/sinkdisc.c
+++ b/libvips/iofuncs/sinkdisc.c
@@ -334,8 +334,10 @@ wbuffer_allocate_fn( VipsThreadState *state, void *a, gboolean *stop )
 			/* Block until the write of the previous buffer 
 			 * is done, then set write of this buffer going.
 			 */
-			if( wbuffer_flush( write ) )
+			if( wbuffer_flush( write ) ) {
+				*stop = TRUE;
 				return( -1 );
+			}
 
 			/* End of image?
 			 */
@@ -359,8 +361,10 @@ wbuffer_allocate_fn( VipsThreadState *state, void *a, gboolean *stop )
 			/* Position buf at the new y.
 			 */
 			if( wbuffer_position( write->buf, 
-				sink_base->y, sink_base->nlines ) )
+				sink_base->y, sink_base->nlines ) ) {
+				*stop = TRUE;
 				return( -1 );
+			}
 		}
 	}