1 files changed, 1 insertions, 1 deletions

diff --git a/lib-src/ebrowse.c b/lib-src/ebrowse.c
index 7fbcba2d63b..b5a9f48946a 100644
--- a/lib-src/ebrowse.c
+++ b/lib-src/ebrowse.c
@@ -2867,7 +2867,7 @@ operator_name (sc)
           MATCH ();
 
           /* If this is a simple operator like `+', stop now.  */
-          if (!isalpha (*s) && *s != '(' && *s != '[')
+          if (!isalpha ((unsigned char) *s) && *s != '(' && *s != '[')
             break;
 
           ++tokens_matched;