diff --git a/src/process.c b/src/process.c
index b201e9b6acc..45ab1fd7245 100644
--- a/src/process.c
+++ b/src/process.c
@@ -2461,6 +2461,10 @@ usage:  (make-pipe-process &rest ARGS)  */)
   /* This may signal an error.  */
   setup_process_coding_systems (proc);
 
+  pset_decoding_buf (p, empty_unibyte_string);
+  eassert (p->decoding_carryover == 0);
+  pset_encoding_buf (p, empty_unibyte_string);
+
   specpdl_ptr = specpdl + specpdl_count;
 
   return proc;