diff --git a/src/borg/platform/posix.pyx b/src/borg/platform/posix.pyx
index 550693605..87640dac6 100644
--- a/src/borg/platform/posix.pyx
+++ b/src/borg/platform/posix.pyx
@@ -6,8 +6,17 @@ from functools import lru_cache
 
 from libc.errno cimport errno as c_errno
 
+from cpython.mem cimport PyMem_Free
+from libc.stddef cimport wchar_t
+
 cdef extern from "wchar.h":
-    cdef int wcswidth(const Py_UNICODE *str, size_t n)
+    # https://www.man7.org/linux/man-pages/man3/wcswidth.3.html
+    cdef int wcswidth(const wchar_t *s, size_t n)
+
+
+cdef extern from "Python.h":
+    # https://docs.python.org/3/c-api/unicode.html#c.PyUnicode_AsWideCharString
+    wchar_t* PyUnicode_AsWideCharString(object, Py_ssize_t*) except NULL
 
 
 def get_errno():
@@ -15,12 +24,14 @@ def get_errno():
 
 
 def swidth(s):
-    str_len = len(s)
-    terminal_width = wcswidth(s, str_len)
+    cdef Py_ssize_t size
+    cdef wchar_t *as_wchar = PyUnicode_AsWideCharString(s, &size)
+    terminal_width = wcswidth(as_wchar, <size_t>size)
+    PyMem_Free(as_wchar)
     if terminal_width >= 0:
         return terminal_width
     else:
-        return str_len
+        return len(s)
 
 
 def process_alive(host, pid, thread):