1 files changed, 3 insertions, 1 deletions

diff --git a/src/editfns.c b/src/editfns.c
index c8b02570c12..ee1249acc11 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3424,7 +3424,9 @@ usage: (format STRING &rest OBJECTS)  */)
            digits to print after the '.' for floats, or the max.
            number of chars to print from a string.  */
 
-        while (*format && index ("-0# ", *format))
+        while (format != end
+               && (*format == '-' || *format == '0' || *format == '#'
+                   || * format == ' '))
           ++format;
 
         if (*format >= '0' && *format <= '9')