diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 073aadb9150..275b1627692 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -21,6 +21,9 @@ Mon Jul  6 22:09:32 1998  Ian Lance Taylor  <ian@cygnus.com>
 
 Mon Jul  6 21:28:14 1998  Jeffrey A Law  (law@cygnus.com)
 
+	* combine.c (expand_compound_operation): Fix thinko in code to optimize
+	(zero_extend:DI (subreg:SI (foo:DI) 0)) to foo:DI.
+
 	* Disable the following change from gcc2.  Not appropriate for egcs:
 
 	Sun Jun  7 09:30:31 1998  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>
diff --git a/gcc/combine.c b/gcc/combine.c
index a299fb098ec..155585b9f1c 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -5203,7 +5203,7 @@ expand_compound_operation (x)
 	  && subreg_lowpart_p (XEXP (x, 0))
 	  && GET_MODE_BITSIZE (GET_MODE (x)) <= HOST_BITS_PER_WIDE_INT
 	  && (nonzero_bits (SUBREG_REG (XEXP (x, 0)), GET_MODE (x))
-	      & ~ GET_MODE_MASK (GET_MODE (SUBREG_REG (x)))) == 0)
+	      & ~ GET_MODE_MASK (GET_MODE (XEXP (x, 0)))) == 0)
 	return SUBREG_REG (XEXP (x, 0));
 
       /* (zero_extend:DI (truncate:SI foo:DI)) is just foo:DI when foo