diff --git a/Help/command/add_custom_command.rst b/Help/command/add_custom_command.rst
index 31565b510d..8d66752274 100644
--- a/Help/command/add_custom_command.rst
+++ b/Help/command/add_custom_command.rst
@@ -357,6 +357,7 @@ The options are:
   Execute the command with the given current working directory.
   If it is a relative path, it will be interpreted relative to the
   build tree directory corresponding to the current source directory.
+  If not specified, set to :variable:`CMAKE_CURRENT_BINARY_DIR`.
 
   This option is currently ignored if ``APPEND`` is given, but a future
   version may use it.
diff --git a/Help/command/add_custom_target.rst b/Help/command/add_custom_target.rst
index b574cbabc4..83fe6b49a8 100644
--- a/Help/command/add_custom_target.rst
+++ b/Help/command/add_custom_target.rst
@@ -191,6 +191,7 @@ The options are:
   Execute the command with the given current working directory.
   If it is a relative path it will be interpreted relative to the
   build tree directory corresponding to the current source directory.
+  If not specified, set to :variable:`CMAKE_CURRENT_BINARY_DIR`.
 
   .. versionadded:: 3.13
     Arguments to ``WORKING_DIRECTORY`` may use
diff --git a/Help/command/execute_process.rst b/Help/command/execute_process.rst
index a2f903699e..37f2b42c2b 100644
--- a/Help/command/execute_process.rst
+++ b/Help/command/execute_process.rst
@@ -75,7 +75,8 @@ Options:
 
 ``WORKING_DIRECTORY``
  The named directory will be set as the current working directory of
- the child processes.
+ the child processes. If not given, the child processes' working directory is
+ unspecified.
 
 ``TIMEOUT``
  After the specified number of seconds (fractions allowed), all unfinished