diff --git a/include/opcode/ChangeLog b/include/opcode/ChangeLog
index e256e6ebd..adf39400c 100644
--- a/include/opcode/ChangeLog
+++ b/include/opcode/ChangeLog
@@ -1,3 +1,7 @@
+2009-02-06  Doug Evans  <dje@google.com>
+
+	* i386.h: Add comment regarding sse* insns and prefixes.
+
 2009-02-03  Sandip Matte  <sandip@rmicorp.com>
 
 	* mips.h (INSN_XLR): Define.
diff --git a/include/opcode/i386.h b/include/opcode/i386.h
index 4311cd640..d60db76b7 100644
--- a/include/opcode/i386.h
+++ b/include/opcode/i386.h
@@ -59,6 +59,11 @@
 /* The opcode for the fwait instruction, which disassembler treats as a
    prefix when it can.  */
 #define FWAIT_OPCODE 0x9b
+
+/* Instruction prefixes.
+   NOTE: For certain SSE* instructions, 0x66,0xf2,0xf3 are treated as
+   part of the opcode.  Other prefixes may still appear between them
+   and the 0x0f part of the opcode.  */
 #define ADDR_PREFIX_OPCODE 0x67
 #define DATA_PREFIX_OPCODE 0x66
 #define LOCK_PREFIX_OPCODE 0xf0