diff --git a/dmoj/cptbox/_cptbox.pyi b/dmoj/cptbox/_cptbox.pyi
index 7a52be6bf..915d74f27 100644
--- a/dmoj/cptbox/_cptbox.pyi
+++ b/dmoj/cptbox/_cptbox.pyi
@@ -12,6 +12,10 @@ PTBOX_ABI_COUNT: int
 ALL_ABIS: List[int]
 SUPPORTED_ABIS: List[int]
 
+class ArgAccessor:
+    def __getitem__(self, reg : int) -> int: ...
+    def __setitem__(self, reg : int, val : int) -> None: ...
+
 class Debugger:
     syscall: int
     result: int
@@ -22,6 +26,7 @@ class Debugger:
     arg3: int
     arg4: int
     arg5: int
+    arg: ArgAccessor
 
     uresult: int
     uarg0: int
@@ -30,6 +35,7 @@ class Debugger:
     uarg3: int
     uarg4: int
     uarg5: int
+    uarg: ArgAccessor
 
     pid: int
     tid: int
diff --git a/dmoj/cptbox/_cptbox.pyx b/dmoj/cptbox/_cptbox.pyx
index c92829669..b218436ac 100644
--- a/dmoj/cptbox/_cptbox.pyx
+++ b/dmoj/cptbox/_cptbox.pyx
@@ -225,6 +225,22 @@ def memory_fd_seal(int fd):
 
 cdef class Process
 
+cdef class Debugger
+
+cdef class ArgAccessor:
+    cdef Debugger debugger
+    cdef object base
+
+    def __cinit__(self, Debugger debugger, object base):
+        self.debugger = debugger
+        self.base = base
+
+    def __getitem__(self, reg):
+        return getattr(self.debugger, '%s%d' % (self.base, reg))
+
+    def __setitem__(self, reg, val):
+        setattr(self.debugger, '%s%d' % (self.base, reg), val)
+
 
 cdef class Debugger:
     cdef pt_debugger *thisptr
@@ -235,6 +251,8 @@ cdef class Debugger:
         self.thisptr = new pt_debugger()
         self.process = process
         self.on_return_callback = {}
+        self.uarg = ArgAccessor(self, "uarg")
+        self.arg = ArgAccessor(self, "arg")
 
     def __dealloc__(self):
         del self.thisptr
diff --git a/dmoj/cptbox/isolate.py b/dmoj/cptbox/isolate.py
index 358948158..c46a54778 100644
--- a/dmoj/cptbox/isolate.py
+++ b/dmoj/cptbox/isolate.py
@@ -213,7 +213,7 @@ def _compile_fs_jail(self, fs) -> FilesystemPolicy:
 
     def _dirfd_getter_from_reg(self, reg: int) -> DirFDGetter:
         def getter(debugger: Debugger) -> int:
-            return getattr(debugger, 'uarg%d' % reg)
+            return debugger.uarg[reg]
 
         return getter
 
@@ -222,7 +222,7 @@ def _dirfd_getter_cwd(self, debugger: Debugger) -> int:
 
     def _fs_jail_getter_from_open_flags_reg(self, reg: int) -> FSJailGetter:
         def getter(debugger: Debugger) -> FilesystemPolicy:
-            open_flags = getattr(debugger, 'uarg%d' % reg)
+            open_flags = debugger.uarg[reg]
             for flag in open_write_flags:
                 # Strict equality is necessary here, since e.g. O_TMPFILE has multiple bits set,
                 # and O_DIRECTORY & O_TMPFILE > 0.
@@ -282,7 +282,7 @@ def check(debugger: Debugger) -> None:
                 # We already allowed this one way or another, don't check again.
                 return
 
-            dirfd = getattr(debugger, 'uarg%d' % dir_reg)
+            dirfd = debugger.uarg[dir_reg]
             full_path = self.get_full_path_unnormalized(debugger, rel_file, dirfd=dirfd)
             self._access_check(debugger, full_path, self.read_fs_jail)
 
@@ -299,9 +299,8 @@ def check(debugger: Debugger) -> None:
         return check
 
     def get_rel_file(self, debugger: Debugger, *, reg: int) -> str:
-        ptr = getattr(debugger, 'uarg%d' % reg)
         try:
-            file = debugger.readstr(ptr)
+            file = debugger.readstr(debugger.uarg[reg])
         except MaxLengthExceeded as e:
             raise DeniedSyscall(ACCESS_ENAMETOOLONG, f'Overly long path: {e.args[0]}')
         except UnicodeDecodeError as e: