diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 88f78305f8dc..8f4c3262d19a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2010-01-14  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/42721
+	Port from no-undefined-overflow branch
+	2009-03-09  Richard Guenther  <rguenther@suse.de>
+
+	* fold-const.c (add_double_with_sign): Fix unsigned overflow
+	detection.
+
 2010-01-14  Richard Guenther  <rguenther@suse.de>
 
 	PR lto/42665
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 9e40296123cd..9d249cc3b2fc 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -326,13 +326,17 @@ add_double_with_sign (unsigned HOST_WIDE_INT l1, HOST_WIDE_INT h1,
   HOST_WIDE_INT h;
 
   l = l1 + l2;
-  h = h1 + h2 + (l < l1);
+  h = (HOST_WIDE_INT) ((unsigned HOST_WIDE_INT) h1
+		       + (unsigned HOST_WIDE_INT) h2
+		       + (l < l1));
 
   *lv = l;
   *hv = h;
 
   if (unsigned_p)
-    return (unsigned HOST_WIDE_INT) h < (unsigned HOST_WIDE_INT) h1;
+    return ((unsigned HOST_WIDE_INT) h < (unsigned HOST_WIDE_INT) h1
+	    || (h == h1
+		&& l < l1));
   else
     return OVERFLOW_SUM_SIGN (h1, h2, h);
 }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index faac669f197a..0478ae577bc9 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2010-01-14  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/42721
+	* gcc.c-torture/execute/pr42721.c: New test.
+
 2010-01-14  Ira Rosen  <irar@il.ibm.com>
 
 	PR tree-optimization/42709
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr42721.c b/gcc/testsuite/gcc.c-torture/execute/pr42721.c
new file mode 100644
index 000000000000..706921b0dbe1
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr42721.c
@@ -0,0 +1,21 @@
+/* PR c/42721 */
+
+extern void abort (void);
+
+static unsigned long long
+foo (unsigned long long x, unsigned long long y)
+{
+  return x / y;
+}
+
+static int a, b;
+
+int
+main (void)
+{
+  unsigned long long c = 1;
+  b ^= c && (foo (a, -1ULL) != 1L);
+  if (b != 1)
+    abort ();
+  return 0;
+}