diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 72414f698ec..c2b7423e0c3 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -202,8 +202,10 @@ always available.
 
 .. data:: executable
 
-   A string giving the name of the executable binary for the Python interpreter, on
-   systems where this makes sense.
+   A string giving the absolute path of the executable binary for the Python
+   interpreter, on systems where this makes sense. If Python is unable to retrieve
+   the real path to its executable, :data:`sys.executable` will be an empty string
+   or ``None``.
 
 
 .. function:: exit([arg])
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 6dc0e422a6d..527e76253e2 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -542,6 +542,9 @@ class SysModuleTest(unittest.TestCase):
         self.assertEqual(out, b'?')
 
     def test_executable(self):
+        # sys.executable should be absolute
+        self.assertEqual(os.path.abspath(sys.executable), sys.executable)
+
         # Issue #7774: Ensure that sys.executable is an empty string if argv[0]
         # has been set to an non existent program name and Python is unable to
         # retrieve the real program name
diff --git a/Misc/NEWS b/Misc/NEWS
index b005e934744..f00738bc946 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -2147,6 +2147,8 @@ C-API
 Documentation
 -------------
 
+- Issue #13402: Document absoluteness of sys.executable.
+
 - Issue #13883: PYTHONCASEOK also works on OS X.
 
 - Issue #12949: Document the kwonlyargcount argument for the PyCode_New
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index d1517d33f6c..955219f2288 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -1257,7 +1257,7 @@ Static objects:\n\
 builtin_module_names -- tuple of module names built into this interpreter\n\
 copyright -- copyright notice pertaining to this interpreter\n\
 exec_prefix -- prefix used to find the machine-specific Python library\n\
-executable -- pathname of this Python interpreter\n\
+executable -- absolute path of the executable binary of the Python interpreter\n\
 float_info -- a struct sequence with information about the float implementation.\n\
 float_repr_style -- string indicating the style of repr() output for floats\n\
 hexversion -- version information encoded as a single integer\n\