diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 70d0eb620f1..1e1f7dca83b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2012-07-07  Ulrich Weigand  <ulrich.weigand@linaro.org>
+
+	* combine.c (force_to_mode) [LSHIFTRT]: Avoid undefined behaviour
+	due to negative shift amount.
+
 2012-07-07  Hans-Peter Nilsson  <hp@axis.com>
 
 	Fix configure test for "stack protector support in target C library".
diff --git a/gcc/combine.c b/gcc/combine.c
index 70b80bca738..ed87f1caa56 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -8433,6 +8433,7 @@ force_to_mode (rtx x, enum machine_mode mode, unsigned HOST_WIDE_INT mask,
 	 in OP_MODE.  */
 
       if (CONST_INT_P (XEXP (x, 1))
+	  && INTVAL (XEXP (x, 1)) >= 0
 	  && INTVAL (XEXP (x, 1)) < HOST_BITS_PER_WIDE_INT
 	  && HWI_COMPUTABLE_MODE_P (op_mode))
 	{