diff --git a/src/arch/x86/isa/formats/cond.isa b/src/arch/x86/isa/formats/cond.isa
new file mode 100644
index 0000000..ab9232b
--- /dev/null
+++ b/src/arch/x86/isa/formats/cond.isa
@@ -0,0 +1,51 @@
+// -*- mode:c++ -*-
+
+// Copyright 2017 Google, Inc.
+//
+// The license below extends only to copyright in the software and shall
+// not be construed as granting a license to any other intellectual
+// property including but not limited to intellectual property relating
+// to a hardware implementation of the functionality of the software
+// licensed hereunder.  You may use the software subject to the license
+// terms below provided that you ensure that this notice is replicated
+// unmodified and in its entirety in all distributions of the software,
+// modified or unmodified, in source code or in binary form.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met: redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer;
+// redistributions in binary form must reproduce the above copyright
+// notice, this list of conditions and the following disclaimer in the
+// documentation and/or other materials provided with the distribution;
+// neither the name of the copyright holders nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Authors: Gabe Black
+
+def format CondInst(cond, *opTypeSet) {{
+    blocks = OutputBlocks()
+
+    if_blocks = specializeInst(Name, list(opTypeSet), EmulEnv())
+    blocks.append(if_blocks)
+    else_blocks = specializeInst('UD2', [], EmulEnv())
+    blocks.append(else_blocks)
+
+    (header_output, decoder_output,
+     decode_block, exec_output) = blocks.makeList()
+    decode_block = '\tif (%s) {\n%s\n\t} else {\n%s\n}\n' % \
+        (cond, if_blocks.decode_block, else_blocks.decode_block)
+}};
diff --git a/src/arch/x86/isa/formats/formats.isa b/src/arch/x86/isa/formats/formats.isa
index b5ffd4d..6aed37f 100644
--- a/src/arch/x86/isa/formats/formats.isa
+++ b/src/arch/x86/isa/formats/formats.isa
@@ -72,3 +72,7 @@
 //Include a format which makes instructions who's sole purpose is to generate
 //a syscall.
 ##include "syscall.isa"
+
+//Include a format which is like Inst, except it conditionally decodes to the
+//specified instruction, or if the condition fails decodes to UD2.
+##include "cond.isa"