1 files changed, 9 insertions, 4 deletions

diff --git a/src/editfns.c b/src/editfns.c
index c1414071c79..3f9618edb08 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3551,10 +3551,15 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                       || float_conversion || conversion == 'i'
                       || conversion == 'o' || conversion == 'x'
                       || conversion == 'X'))
-            error ("Invalid format operation %%%c",
-                   multibyte_format
-                   ? STRING_CHAR ((unsigned char *) format - 1)
-                   : *((unsigned char *) format - 1));
+            {
+              unsigned char *p = (unsigned char *) format - 1;
+              if (multibyte_format)
+                error ("Invalid format operation %%%c", STRING_CHAR (p));
+              else
+                error (*p <= 127 ? "Invalid format operation %%%c"
+                                 : "Invalid format operation char #o%03o",
+                       *p);
+            }
           else if (! (FIXNUMP (arg) || ((BIGNUMP (arg) || FLOATP (arg))
                                         && conversion != 'c')))
             error ("Format specifier doesn't match argument type");