diff --git a/src/arch/x86/isa/decoder/one_byte_opcodes.isa b/src/arch/x86/isa/decoder/one_byte_opcodes.isa
index b5f77cd31e..04b3adce1f 100644
--- a/src/arch/x86/isa/decoder/one_byte_opcodes.isa
+++ b/src/arch/x86/isa/decoder/one_byte_opcodes.isa
@@ -483,7 +483,7 @@
             0x0: LOOPNE(Jb);
             0x1: LOOPE(Jb);
             0x2: LOOP(Jb);
-            0x3: JRCX(Jb);
+            0x3: JRCXZ(Jb);
             0x4: IN(rAb,Ib);
             0x5: IN(rAv,Iv);
             0x6: OUT(Ib,rAb);
diff --git a/src/arch/x86/isa/insts/general_purpose/control_transfer/conditional_jump.py b/src/arch/x86/isa/insts/general_purpose/control_transfer/conditional_jump.py
index 390a08b3c3..d0fa31a5a6 100644
--- a/src/arch/x86/isa/insts/general_purpose/control_transfer/conditional_jump.py
+++ b/src/arch/x86/isa/insts/general_purpose/control_transfer/conditional_jump.py
@@ -210,8 +210,10 @@ def macroop JNO_I
     wrip t1, t2, flags=(nCOF,)
 };
 
-def macroop JRCX_I
+def macroop JRCXZ_I
 {
+    # Make the default data size of jumps 64 bits in 64 bit mode
+    .adjust_env oszIn64Override
     .control_direct
 
     rdip t1