2 files changed, 5 insertions, 2 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 79d9b636e09..b9cf18cedd9 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,8 @@
 2011-06-18  Paul Eggert  <eggert@cs.ucla.edu>
 
+        * fns.c (concat): Catch string overflow earlier.
+        Do not rely on integer wraparound.
+
         * dispextern.h (struct it.overlay_strings_charpos): EMACS_INT, not int.
 
 2011-06-17  Paul Eggert  <eggert@cs.ucla.edu>
diff --git a/src/fns.c b/src/fns.c
index a19c886e3e1..4c1505ab0f1 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -565,8 +565,8 @@ concat (ptrdiff_t nargs, Lisp_Object *args,
         }
 
       result_len += len;
-      if (result_len < 0)
-        error ("String overflow");
+      if (STRING_BYTES_BOUND < result_len)
+        string_overflow ();
     }
 
   if (! some_multibyte)