diff --git a/docs/doc-collection/opcodes/x86/8086.dop b/docs/doc-collection/opcodes/x86/8086.dop
index 5522f6962..7ec57324a 100644
--- a/docs/doc-collection/opcodes/x86/8086.dop
+++ b/docs/doc-collection/opcodes/x86/8086.dop
@@ -290,3 +290,19 @@ define register map "sreg" {
     /* no index 7 */
 }
 
+define encoding "mrm" {
+    description "mod/reg/rm field as encoded in instruction";
+    type uint8_t;
+    subset "mod" bit range(7:6);
+    subset "reg" bit range(5:3);
+    subset "rm"  bit range(2:0);
+}
+
+define encoding "sib" {
+    description "scale/index/base field as encoded in instruction";
+    type uint8_t;
+    subset "scale" bit range(7:6);
+    subset "index" bit range(5:3);
+    subset "base"  bit range(2:0);
+}
+