diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 95987efeb56..38dd30edfe1 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2007-02-02  Ian Lance Taylor  <iant@google.com>
+
+	* expmed.c (expand_divmod): Add comment.
+
 2007-02-02  Kazu Hirata  <kazu@codesourcery.com>
 
 	* emit-rtl.c (renumber_insns): Remove.
diff --git a/gcc/expmed.c b/gcc/expmed.c
index fea859a18c1..8e8a63917a1 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -4176,6 +4176,9 @@ expand_divmod (int rem_flag, enum tree_code code, enum machine_mode mode,
 		HOST_WIDE_INT d = INTVAL (op1);
 		unsigned HOST_WIDE_INT abs_d;
 
+		/* Since d might be INT_MIN, we have to cast to
+		   unsigned HOST_WIDE_INT before negating to avoid
+		   undefined signed overflow.  */
 		abs_d = (d >= 0
 			 ? (unsigned HOST_WIDE_INT) d
 			 : - (unsigned HOST_WIDE_INT) d);