1 files changed, 2 insertions, 0 deletions

diff --git a/src/coding.c b/src/coding.c
index 47bfbf5cacb..12558b958c4 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -6333,6 +6333,8 @@ about coding-system objects.  */)
     return Qt;
   if (!SYMBOLP (obj))
     return Qnil;
+  if (! NILP (Fget (obj, Qcoding_system_define_form)))
+    return Qt;
   /* Get coding-spec vector for OBJ.  */
   obj = Fget (obj, Qcoding_system);
   return ((VECTORP (obj) && XVECTOR (obj)->size == 5)