diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 81d0b997c41..86b58686fc9 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,9 @@
 2004-12-31  Hans-Peter Nilsson  <hp@bitrange.com>
 
+	PR target/18701
+	* combine.c (combine_simplify_rtx): Do not allow paradoxical
+	subregs of MEM.
+
 	PR target/18701
 	* combine.c (gen_lowpart_for_combine): When stripping SUBREG of
 	MEM, adjust imode and isize.
diff --git a/gcc/combine.c b/gcc/combine.c
index 61b93dd3048..90934e11672 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -3983,10 +3983,14 @@ combine_simplify_rtx (rtx x, enum machine_mode op0_mode, int in_dest)
       }
 
       /* Don't change the mode of the MEM if that would change the meaning
-	 of the address.  */
+	 of the address.  Similarly, don't allow widening, as that may
+	 access memory outside the defined object or using an address
+	 that is invalid for a wider mode.  */
       if (MEM_P (SUBREG_REG (x))
 	  && (MEM_VOLATILE_P (SUBREG_REG (x))
-	      || mode_dependent_address_p (XEXP (SUBREG_REG (x), 0))))
+	      || mode_dependent_address_p (XEXP (SUBREG_REG (x), 0))
+	      || (GET_MODE_SIZE (mode)
+		  > GET_MODE_SIZE (GET_MODE (SUBREG_REG (x))))))
 	return gen_rtx_CLOBBER (mode, const0_rtx);
 
       /* Note that we cannot do any narrowing for non-constants since