diff --git a/doc-collection/opcodes/x86/8086.dop b/doc-collection/opcodes/x86/8086.dop
index 262e5902e..3bed0d036 100644
--- a/doc-collection/opcodes/x86/8086.dop
+++ b/doc-collection/opcodes/x86/8086.dop
@@ -378,4 +378,24 @@ opcode sequence([0x91,0x97]) name "XCHG" {
     reg index = opbyte(0) & 7;
     common opcode "XCHG" param(regw,accum);
 }
+opcode sequence(0x98) name "CBW" if datasize == 16 {
+    /* AX = sign extended AL */
+    input AL;
+    output AX;
+}
+opcode sequence(0x98) name "CWDE" if datasize == 32 {
+    /* EAX = sign extended AX */
+    input AX;
+    output EAX;
+}
+opcode sequence(0x99) name "CWD" if datasize == 16 {
+    /* DX:AX = sign extended AX */
+    input AX;
+    output DX,AX;
+}
+opcode sequence(0x99) name "CDQ" if datasize == 32 {
+    /* EDX:EAX = sign extended EAX */
+    input EAX;
+    output EDX,EAX;
+}