diff --git a/bochs/cpu/mmx.cc b/bochs/cpu/mmx.cc
index 245d03a5b..5ea4a8e5b 100644
--- a/bochs/cpu/mmx.cc
+++ b/bochs/cpu/mmx.cc
@@ -1,5 +1,5 @@
 /////////////////////////////////////////////////////////////////////////
-// $Id: mmx.cc,v 1.87 2009-10-24 11:17:51 sshwarts Exp $
+// $Id: mmx.cc,v 1.88 2009-11-13 09:55:22 sshwarts Exp $
 /////////////////////////////////////////////////////////////////////////
 //
 //   Copyright (c) 2002-2009 Stanislav Shwartsman
@@ -2617,11 +2617,11 @@ void BX_CPP_AttrRegparmN(1) BX_CPU_C::MASKMOVQ_PqPRq(bxInstruction_c *i)
       rdi = DI;
   }
 
-  if (MMXUQ(mask) == 0) return;
-
   /* do read-modify-write for efficiency */
   MMXUQ(tmp) = read_RMW_virtual_qword(i->seg(), rdi);
 
+  if (MMXUQ(mask) == 0) return;
+
   if(MMXUB0(mask) & 0x80) MMXUB0(tmp) = MMXUB0(op);
   if(MMXUB1(mask) & 0x80) MMXUB1(tmp) = MMXUB1(op);
   if(MMXUB2(mask) & 0x80) MMXUB2(tmp) = MMXUB2(op);
diff --git a/bochs/cpu/sse_move.cc b/bochs/cpu/sse_move.cc
index 69ffe3e8a..0cf3ec2d3 100644
--- a/bochs/cpu/sse_move.cc
+++ b/bochs/cpu/sse_move.cc
@@ -1,5 +1,5 @@
 /////////////////////////////////////////////////////////////////////////
-// $Id: sse_move.cc,v 1.102 2009-10-27 20:03:35 sshwarts Exp $
+// $Id: sse_move.cc,v 1.103 2009-11-13 09:55:22 sshwarts Exp $
 /////////////////////////////////////////////////////////////////////////
 //
 //   Copyright (c) 2003-2009 Stanislav Shwartsman
@@ -832,12 +832,12 @@ void BX_CPP_AttrRegparmN(1) BX_CPU_C::MASKMOVDQU_VdqUdq(bxInstruction_c *i)
       rdi = DI;
   }
 
-  /* no data will be written to memory if mask is all 0s */
-  if ((mask.xmm64u(0) | mask.xmm64u(1)) == 0) return;
-
   /* implement as read-modify-write for efficiency */
   read_virtual_dqword(i->seg(), rdi, (Bit8u *) &temp);
 
+  /* no data will be written to memory if mask is all 0s */
+  if ((mask.xmm64u(0) | mask.xmm64u(1)) == 0) return;
+
   for(unsigned j=0; j<16; j++) {
     if(mask.xmmubyte(j) & 0x80) temp.xmmubyte(j) = op.xmmubyte(j);
   }