diff --git a/kitty_tests/glfw.py b/kitty_tests/glfw.py
index 25ecb5fe3..0c531f8ee 100644
--- a/kitty_tests/glfw.py
+++ b/kitty_tests/glfw.py
@@ -19,8 +19,14 @@ class TestGLFW(BaseTest):
 
         backend_utils = glfw_path('x11')
         lib = ctypes.CDLL(backend_utils)
+        libc = ctypes.CDLL(None)
+
+        class allocated_c_char_p(ctypes.c_char_p):
+            def __del__(self):
+                libc.free(self)
+
         utf_8_strndup = lib.utf_8_strndup
-        utf_8_strndup.restype = ctypes.c_char_p
+        utf_8_strndup.restype = allocated_c_char_p
         utf_8_strndup.argtypes = (ctypes.c_char_p, ctypes.c_size_t)
 
         def test(string):
@@ -32,14 +38,14 @@ class TestGLFW(BaseTest):
                 part_bytes = bytes(part, 'utf-8')
                 length_bytes = len(part_bytes)
                 for length_bytes_2 in range(prev_length_bytes + 1, length_bytes):
-                    self.ae(utf_8_strndup(string_bytes, length_bytes_2), prev_part_bytes)
-                self.ae(utf_8_strndup(string_bytes, length_bytes), part_bytes)
+                    self.ae(utf_8_strndup(string_bytes, length_bytes_2).value, prev_part_bytes)
+                self.ae(utf_8_strndup(string_bytes, length_bytes).value, part_bytes)
                 prev_part_bytes = part_bytes
                 prev_length_bytes = length_bytes
-            self.ae(utf_8_strndup(string_bytes, len(string_bytes) + 1), string_bytes)  # Try to go one character after the end of the string
+            self.ae(utf_8_strndup(string_bytes, len(string_bytes) + 1).value, string_bytes)  # Try to go one character after the end of the string
 
-        self.ae(utf_8_strndup(None, 2), None)
-        self.ae(utf_8_strndup(b'', 2), b'')
+        self.ae(utf_8_strndup(None, 2).value, None)
+        self.ae(utf_8_strndup(b'', 2).value, b'')
 
         test('ö')
         test('>a<')