diff --git a/src/browser/starter.js b/src/browser/starter.js
index ce0bb006..a63ee3e2 100644
--- a/src/browser/starter.js
+++ b/src/browser/starter.js
@@ -213,7 +213,6 @@ function V86Starter(options)
         "verw": function() { return cpu.verw.apply(cpu, arguments); },
         "verr": function() { return cpu.verr.apply(cpu, arguments); },
 
-        "update_cs_size": function() { return cpu.update_cs_size.apply(cpu, arguments); },
         "cpuid": function() { return cpu.cpuid.apply(cpu, arguments); },
 
         "load_ldt": function() { return cpu.load_ldt.apply(cpu, arguments); },
diff --git a/src/native/js_imports.h b/src/native/js_imports.h
index 61feb516..a32f43f4 100644
--- a/src/native/js_imports.h
+++ b/src/native/js_imports.h
@@ -44,7 +44,6 @@ extern void popa16(void);
 extern void popa32(void);
 extern void undefined_instruction(void);
 extern void unimplemented_sse(void);
-extern void update_cs_size(int32_t);
 extern void update_eflags(int32_t);
 extern bool switch_seg(int32_t, int32_t);
 extern void lss16(int32_t, int32_t, int32_t);
diff --git a/src/rust/cpu2/cpu.rs b/src/rust/cpu2/cpu.rs
index 4b221b36..0e95bd17 100644
--- a/src/rust/cpu2/cpu.rs
+++ b/src/rust/cpu2/cpu.rs
@@ -921,6 +921,14 @@ pub unsafe fn cpl_changed() {
     *last_virt_esp = -1;
 }
 
+pub unsafe fn update_cs_size(new_size: bool) {
+    if *is_32 != new_size {
+        *is_32 = new_size;
+        // TODO:
+        // update_operand_size();
+    }
+}
+
 pub unsafe fn test_privileges_for_io(port: i32, size: i32) -> bool {
     if *protected_mode && (*cpl > getiopl() as u8 || (*flags & FLAG_VM != 0)) {
         if !*tss_size_32 {
diff --git a/src/rust/cpu2/instructions_0f.rs b/src/rust/cpu2/instructions_0f.rs
index 1221a389..2eb4a487 100644
--- a/src/rust/cpu2/instructions_0f.rs
+++ b/src/rust/cpu2/instructions_0f.rs
@@ -21,8 +21,6 @@ extern "C" {
     #[no_mangle]
     fn cpuid();
     #[no_mangle]
-    fn update_cs_size(cs_size: bool);
-    #[no_mangle]
     fn lsl(r: i32, v: i32) -> i32;
     #[no_mangle]
     fn lar(r: i32, v: i32) -> i32;