1 files changed, 1 insertions, 0 deletions
diff --git a/io.c b/io.c
index 19690ddc4d..87caa7651f 100644
--- a/io.c
+++ b/io.c
@@ -1315,6 +1315,7 @@ rb_io_ungetc(io, c)
 
     GetOpenFile(io, fptr);
     rb_io_check_readable(fptr);
+    flush_before_seek(fptr);
 
     if (ungetc(cc, fptr->f) == EOF && cc != EOF)
 	rb_sys_fail(fptr->path);