diff --git a/opcodes/ChangeLog b/opcodes/ChangeLog
index 522d81bd66..4f56e1385b 100644
--- a/opcodes/ChangeLog
+++ b/opcodes/ChangeLog
@@ -1,3 +1,9 @@
+2020-07-29  Andreas Arnez  <arnez@linux.ibm.com>
+
+	* s390-mkopc.c (insertExpandedMnemonic): Handle unreachable
+	default case with abort() instead of printing an error message and
+	continuing, to avoid a maybe-uninitialized warning.
+
 2020-07-24  Nick Clifton  <nickc@redhat.com>
 
 	* po/de.po: Updated German translation.
diff --git a/opcodes/s390-mkopc.c b/opcodes/s390-mkopc.c
index c593fb6079..b6c49e6d1e 100644
--- a/opcodes/s390-mkopc.c
+++ b/opcodes/s390-mkopc.c
@@ -240,7 +240,8 @@ insertExpandedMnemonic (char *opcode, char *mnemonic, char *format,
       ext_table = s390_crb_extensions;
       ext_table_length = NUM_CRB_EXTENSIONS;
       break;
-    default: fprintf (stderr, "Unknown tag char: %c\n", *tag);
+    default:
+      abort ();			/* Should be unreachable.  */
     }
 
   for (i = 0; i < ext_table_length; i++)