diff --git a/Help/command/function.rst b/Help/command/function.rst
index 069f9fa792..6722ca417b 100644
--- a/Help/command/function.rst
+++ b/Help/command/function.rst
@@ -59,20 +59,29 @@ Arguments
 
 When the function is invoked, the recorded ``<commands>`` are first
 modified by replacing formal parameters (``${arg1}``, ...) with the
-arguments passed, and then invoked as normal commands.
+arguments passed, and then invoked as normal commands. The following
+variables are set in the scope of the function:
 
-In addition to referencing the formal parameters you can reference the
-``ARGC`` variable which will be set to the number of arguments passed
-into the function as well as ``ARGV0``, ``ARGV1``, ``ARGV2``, ...  which
-will have the actual values of the arguments passed in.  This facilitates
-creating functions with optional arguments.
+``ARGC``
+  The number of arguments passed into the function.
 
-Furthermore, ``ARGV`` holds the list of all arguments given to the
-function and ``ARGN`` holds the list of arguments past the last expected
-argument.  Referencing to ``ARGV#`` arguments beyond ``ARGC`` have
-undefined behavior.  Checking that ``ARGC`` is greater than ``#`` is
-the only way to ensure that ``ARGV#`` was passed to the function as an
-extra argument.
+``ARGV``
+  The list of all arguments given to the function.
+
+``ARGV#``
+  The variables ``ARGV0``, ``ARGV1``, ``ARGV2``, ...  which will have the
+  actual values of the arguments passed in. References to ``ARGV#``
+  arguments beyond ``ARGC`` have undefined behavior.  Checking that
+  ``ARGC`` is greater than ``#`` is the only way to ensure that ``ARGV#``
+  was passed to the function as an extra argument.
+
+``ARGN``
+  The list of arguments past the last expected argument.
+
+``ARGNC``
+  .. versionadded:: 4.5
+
+  The number of arguments past the last expected argument.
 
 See Also
 ^^^^^^^^
diff --git a/Help/release/dev/function-argnc.rst b/Help/release/dev/function-argnc.rst
new file mode 100644
index 0000000000..94210e0a88
--- /dev/null
+++ b/Help/release/dev/function-argnc.rst
@@ -0,0 +1,5 @@
+function-argnc
+--------------
+
+* The :command:`function` command now sets the ``ARGNC`` variable, which
+  holds the number of arguments past the last expected argument.
diff --git a/Source/cmFunctionCommand.cxx b/Source/cmFunctionCommand.cxx
index 3e62649c89..0d029938fb 100644
--- a/Source/cmFunctionCommand.cxx
+++ b/Source/cmFunctionCommand.cxx
@@ -25,7 +25,7 @@
 
 namespace {
 std::string const ARGC = "ARGC";
-std::string const kFUNCTION_ARGNC = "_FUNCTION_ARGNC";
+std::string const ARGNC = "ARGNC";
 std::string const ARGN = "ARGN";
 std::string const ARGV = "ARGV";
 std::string const CMAKE_CURRENT_FUNCTION = "CMAKE_CURRENT_FUNCTION";
@@ -94,7 +94,7 @@ bool cmFunctionHelperCommand::operator()(
     makefile.AddDefinition(this->Args[j], expandedArgs[j - 1]);
   }
 
-  // define ARGV, ARGN, and _FUNCTION_ARGNC
+  // define ARGV, ARGN, and ARGNC
   auto const argvDef = cmList::to_string(expandedArgs);
   auto const expIt = expandedArgs.begin() + (this->Args.size() - 1);
   auto const argnDef =
@@ -105,8 +105,8 @@ bool cmFunctionHelperCommand::operator()(
   makefile.MarkVariableAsUsed(ARGV);
   makefile.AddDefinition(ARGN, argnDef);
   makefile.MarkVariableAsUsed(ARGN);
-  makefile.AddDefinition(kFUNCTION_ARGNC, functionArgncDef);
-  makefile.MarkVariableAsUsed(kFUNCTION_ARGNC);
+  makefile.AddDefinition(ARGNC, functionArgncDef);
+  makefile.MarkVariableAsUsed(ARGNC);
 
   makefile.AddDefinition(CMAKE_CURRENT_FUNCTION, this->Args.front());
   makefile.MarkVariableAsUsed(CMAKE_CURRENT_FUNCTION);
diff --git a/Source/cmParseArgumentsCommand.cxx b/Source/cmParseArgumentsCommand.cxx
index 88b62952a8..19f23eed15 100644
--- a/Source/cmParseArgumentsCommand.cxx
+++ b/Source/cmParseArgumentsCommand.cxx
@@ -182,12 +182,11 @@ bool cmParseArgumentsCommand(std::vector<std::string> const& args,
     }
     parseFromArg = true;
     argIter++; // move past PARSE_ARGN
-    std::string argncStr =
-      status.GetMakefile().GetSafeDefinition("_FUNCTION_ARGNC");
+    std::string argncStr = status.GetMakefile().GetSafeDefinition("ARGNC");
     if (!cmStrToULong(argncStr, &argnc)) {
       status.GetMakefile().IssueMessage(
         MessageType::FATAL_ERROR,
-        cmStrCat("PARSE_ARGN called with _FUNCTION_ARGNC='", argncStr,
+        cmStrCat("PARSE_ARGN called with ARGNC='", argncStr,
                  "' that is not an unsigned integer"));
       cmSystemTools::SetFatalErrorOccurred();
       return true;
diff --git a/Tests/RunCMake/cmake_parse_arguments/BadArgN2-stderr.txt b/Tests/RunCMake/cmake_parse_arguments/BadArgN2-stderr.txt
index 806756a379..dcb6341ab4 100644
--- a/Tests/RunCMake/cmake_parse_arguments/BadArgN2-stderr.txt
+++ b/Tests/RunCMake/cmake_parse_arguments/BadArgN2-stderr.txt
@@ -1,5 +1,5 @@
 ^CMake Error at BadArgN2\.cmake:[0-9]+ \(cmake_parse_arguments\):
-  PARSE_ARGN called with _FUNCTION_ARGNC='' that is not an unsigned integer
+  PARSE_ARGN called with ARGNC='' that is not an unsigned integer
 Call Stack \(most recent call first\):
   BadArgN2\.cmake:[0-9]+ \(test2\)
   CMakeLists\.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/cmake_parse_arguments/BadArgN2.cmake b/Tests/RunCMake/cmake_parse_arguments/BadArgN2.cmake
index 0e916791c4..476d0bca22 100644
--- a/Tests/RunCMake/cmake_parse_arguments/BadArgN2.cmake
+++ b/Tests/RunCMake/cmake_parse_arguments/BadArgN2.cmake
@@ -1,5 +1,5 @@
 function(test2)
-  unset(_FUNCTION_ARGNC)
+  unset(ARGNC)
   cmake_parse_arguments(PARSE_ARGN pref "" "" "")
 endfunction()
 test2()