diff --git a/src/ChangeLog b/src/ChangeLog
index 011f5beefe0..5f18c8d0062 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,15 @@
 2011-06-16  Paul Eggert  <eggert@cs.ucla.edu>
 
+	Improve buffer-overflow checking.
+	* fileio.c (Finsert_file_contents):
+	* insdel.c (insert_from_buffer_1, replace_range, replace_range_2):
+	Remove the old (too-loose) buffer overflow checks.
+	They weren't needed, since make_gap checks for buffer overflow.
+	* insdel.c (make_gap_larger): Catch buffer overflows that were missed.
+	The old code merely checked for Emacs fixnum overflow, and relied
+	on undefined (wraparound) behavior.  The new code avoids undefined
+	behavior, and also checks for ptrdiff_t and/or size_t overflow.
+
 	* editfns.c (Finsert_char): Don't dump core with very negative counts.
 	Tune.  Don't use wider integers than needed.  Don't use alloca.
 	Use a bigger 'string' buffer.  Rewrite to avoid 'n > 0' test.
diff --git a/src/fileio.c b/src/fileio.c
index 4458a3a4807..dd34872c263 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3800,16 +3800,7 @@ variable `last-coding-system-used' to the coding system actually used.  */)
     }
 
   if (! not_regular)
-    {
-      register Lisp_Object temp;
-
-      total = XINT (end) - XINT (beg);
-
-      /* Make sure point-max won't overflow after this insertion.  */
-      XSETINT (temp, total);
-      if (total != XINT (temp))
-	buffer_overflow ();
-    }
+    total = XINT (end) - XINT (beg);
   else
     /* For a special file, all we can do is guess.  */
     total = READ_BUF_SIZE;
diff --git a/src/insdel.c b/src/insdel.c
index ca53177a3e1..bc95e3ad9e8 100644
--- a/src/insdel.c
+++ b/src/insdel.c
@@ -406,16 +406,16 @@ make_gap_larger (EMACS_INT nbytes_added)
   EMACS_INT real_gap_loc;
   EMACS_INT real_gap_loc_byte;
   EMACS_INT old_gap_size;
+  EMACS_INT current_size = Z_BYTE - BEG_BYTE + GAP_SIZE;
+  enum { enough_for_a_while = 2000 };
 
-  /* If we have to get more space, get enough to last a while.  */
-  nbytes_added += 2000;
+  if (BUF_BYTES_MAX - current_size < nbytes_added)
+    buffer_overflow ();
 
-  { EMACS_INT total_size = Z_BYTE - BEG_BYTE + GAP_SIZE + nbytes_added;
-    if (total_size < 0
-	/* Don't allow a buffer size that won't fit in a Lisp integer.  */
-	|| total_size != XINT (make_number (total_size)))
-      buffer_overflow ();
-  }
+  /* If we have to get more space, get enough to last a while;
+     but do not exceed the maximum buffer size.  */
+  nbytes_added = min (nbytes_added + enough_for_a_while,
+		      BUF_BYTES_MAX - current_size);
 
   enlarge_buffer_text (current_buffer, nbytes_added);
 
@@ -1069,7 +1069,6 @@ static void
 insert_from_buffer_1 (struct buffer *buf,
 		      EMACS_INT from, EMACS_INT nchars, int inherit)
 {
-  register Lisp_Object temp;
   EMACS_INT chunk, chunk_expanded;
   EMACS_INT from_byte = buf_charpos_to_bytepos (buf, from);
   EMACS_INT to_byte = buf_charpos_to_bytepos (buf, from + nchars);
@@ -1108,11 +1107,6 @@ insert_from_buffer_1 (struct buffer *buf,
       outgoing_nbytes = outgoing_before_gap + outgoing_after_gap;
     }
 
-  /* Make sure point-max won't overflow after this insertion.  */
-  XSETINT (temp, outgoing_nbytes + Z);
-  if (outgoing_nbytes + Z != XINT (temp))
-    buffer_overflow ();
-
   /* Do this before moving and increasing the gap,
      because the before-change hooks might move the gap
      or make it smaller.  */
@@ -1309,7 +1303,6 @@ replace_range (EMACS_INT from, EMACS_INT to, Lisp_Object new,
   EMACS_INT insbytes = SBYTES (new);
   EMACS_INT from_byte, to_byte;
   EMACS_INT nbytes_del, nchars_del;
-  register Lisp_Object temp;
   struct gcpro gcpro1;
   INTERVAL intervals;
   EMACS_INT outgoing_insbytes = insbytes;
@@ -1353,11 +1346,6 @@ replace_range (EMACS_INT from, EMACS_INT to, Lisp_Object new,
     outgoing_insbytes
       = count_size_as_multibyte (SDATA (new), insbytes);
 
-  /* Make sure point-max won't overflow after this insertion.  */
-  XSETINT (temp, Z_BYTE - nbytes_del + outgoing_insbytes);
-  if (Z_BYTE - nbytes_del + outgoing_insbytes != XINT (temp))
-    buffer_overflow ();
-
   GCPRO1 (new);
 
   /* Make sure the gap is somewhere in or next to what we are deleting.  */
@@ -1488,7 +1476,6 @@ replace_range_2 (EMACS_INT from, EMACS_INT from_byte,
 		 int markers)
 {
   EMACS_INT nbytes_del, nchars_del;
-  Lisp_Object temp;
 
   CHECK_MARKERS ();
 
@@ -1498,11 +1485,6 @@ replace_range_2 (EMACS_INT from, EMACS_INT from_byte,
   if (nbytes_del <= 0 && insbytes == 0)
     return;
 
-  /* Make sure point-max won't overflow after this insertion.  */
-  XSETINT (temp, Z_BYTE - nbytes_del + insbytes);
-  if (Z_BYTE - nbytes_del + insbytes != XINT (temp))
-    buffer_overflow ();
-
   /* Make sure the gap is somewhere in or next to what we are deleting.  */
   if (from > GPT)
     gap_right (from, from_byte);