diff --git a/src/arch/x86/isa/bitfields.isa b/src/arch/x86/isa/bitfields.isa
index fff324caa..e4a5e310c 100644
--- a/src/arch/x86/isa/bitfields.isa
+++ b/src/arch/x86/isa/bitfields.isa
@@ -85,3 +85,5 @@ def bitfield SIB sib;
 def bitfield SIB_SCALE sib.scale;
 def bitfield SIB_INDEX sib.index;
 def bitfield SIB_BASE sib.base;
+
+def bitfield OPSIZE opSize;