--- b/.circleci/config.yml
+++ a/.circleci/config.yml
@@ -22,7 +22,7 @@
     run:
       name: Dependencies
       command: |
+        sudo apt-get install -y rsync lua5.1 ccache kwstyle
-        sudo apt-get install -y rsync lua5.3 ccache kwstyle
         sudo python -m pip install --upgrade pip
         sudo python -m pip install scikit-ci-addons # Provides "ctest_junit_formatter" add-on
         sudo python -m pip install cmake==3.13.3
--- b/.travis.yml
+++ a/.travis.yml
@@ -19,7 +19,7 @@
       sudo: required
 
 before_script:
+  - sudo apt-get remove cmake && sudo apt-get install swig lua5.1 libinsighttoolkit4-dev doxygen graphviz
-  - sudo apt-get remove cmake && sudo apt-get install swig lua5.3 libinsighttoolkit4-dev doxygen graphviz
   - cd ${ExternalData_OBJECT_STORES} && if [[ ! -e ${CMAKE_DOWNLOAD_FILE} ]]; then curl -sSO https://cmake.org/files/v3.6/${CMAKE_DOWNLOAD_FILE}; fi
   - echo "y\n" | sudo bash "${ExternalData_OBJECT_STORES}/${CMAKE_DOWNLOAD_FILE}" --prefix=/usr/local --exclude-subdir
   - cmake --version
--- b/CMake/sitkGenerateFilterSource.cmake
+++ a/CMake/sitkGenerateFilterSource.cmake
@@ -6,7 +6,7 @@
   get_property( SAVE_LUA_EXECUTABLE_TYPE CACHE LUA_EXECUTABLE PROPERTY TYPE )
   get_property( SAVE_LUA_EXECUTABLE_DOCSTRING CACHE LUA_EXECUTABLE PROPERTY HELPSTRING )
 
+  find_package( LuaInterp 5.1  REQUIRED )
-  find_package( LuaInterp 5.3  REQUIRED )
   set( SimpleITK_LUA_EXECUTABLE ${LUA_EXECUTABLE} CACHE PATH "Lua executable used for code generation." )
 
   if (DEFINED SAVE_LUA_EXECUTABLE)
@@ -45,10 +45,10 @@
 
 if( SITK_LUA_VERSION_RESULT_VARIABLE
       OR
+    NOT ${SimpleITK_LUA_EXECUTABLE_VERSION} VERSION_GREATER "5.1"
-    NOT ${SimpleITK_LUA_EXECUTABLE_VERSION} VERSION_GREATER "5.3"
       OR
+    NOT ${SimpleITK_LUA_EXECUTABLE_VERSION} VERSION_LESS "5.2" )
+  message(SEND_ERROR "Lua version 5.1 is required for SimpleITK_LUA_EXECUTABLE_VERSION.")
-    NOT ${SimpleITK_LUA_EXECUTABLE_VERSION} VERSION_LESS "5.4" )
-  message(SEND_ERROR "Lua version 5.3 is required for SimpleITK_LUA_EXECUTABLE_VERSION.")
 endif()
 
 # Sets "out_var" variable name to the value in the json path specified
--- b/ExpandTemplateGenerator/Components/ExecuteInternalSetITKFilterInputs.cxx.in
+++ a/ExpandTemplateGenerator/Components/ExecuteInternalSetITKFilterInputs.cxx.in
@@ -8,7 +8,7 @@
 $(if inputs then
 for i = 1,#inputs do
   if inputs[i].optional then
+    OUT = OUT .. '  if ( in'..inputs[i].name..' != NULL )\  {\n  '
-    OUT = OUT .. '  if ( in'..inputs[i].name..' != NULL ) {\n'
   else
     OUT = OUT .. '  assert( '..'in' .. inputs[i].name ..' != NULL );\n'
   end
--- b/ExpandTemplateGenerator/ExpandTemplate.lua
+++ a/ExpandTemplateGenerator/ExpandTemplate.lua
@@ -9,30 +9,14 @@
 local pop     = table.remove
 local concat  = table.concat
 
--- based on http://lua-users.org/lists/lua-l/2010-06/msg00314.html
--- this assumes f is a function
-local function findenv(f)
-  local level = 1
-  repeat
-    local name, value = debug.getupvalue(f, level)
-    if name == '_ENV' then return level, value end
-    level = level + 1
-  until name == nil
-  return nil end
-getfenv = function (f) return(select(2, findenv(f)) or _G) end
-setfenv = function (f, t)
-  local level = findenv(f)
-  if level then debug.setupvalue(f, level, t) end
-  return f end
-
 local statements = {}
+for w in string.gfind('do if for while repeat', '%a+') do
-for w in string.gmatch('do if for while repeat', '%a+') do
   statements[w] = true
 end
 
 function expand(str, ...)
   assert(type(str)=='string', 'expecting string')
+  local searchlist = arg
-  local searchlist = table.pack(...)
   local estring,evar
 
   function estring(str)
--- b/SuperBuild/External_Lua.cmake
+++ a/SuperBuild/External_Lua.cmake
@@ -7,7 +7,7 @@
 
 set(proj Lua)
 
+set(lua_TARGET_VERSION 5.1.5)
-set(lua_TARGET_VERSION 5.3.5)
 
 # follow the standard EP_PREFIX locations
 set(lua_binary_dir ${CMAKE_CURRENT_BINARY_DIR}/${proj}-prefix/src/${proj}-build)
--- b/SuperBuild/SuperBuild.cmake
+++ a/SuperBuild/SuperBuild.cmake
@@ -307,11 +307,11 @@
 #------------------------------------------------------------------------------
 # Lua
 #------------------------------------------------------------------------------
+option ( SimpleITK_USE_SYSTEM_LUA "Use a pre-compiled version of LUA 5.1 previously configured for your system" OFF )
-option ( SimpleITK_USE_SYSTEM_LUA "Use a pre-compiled version of LUA 5.3 previously configured for your system" OFF )
 sitk_legacy_naming( SimpleITK_USE_SYSTEM_LUA USE_SYSTEM_LUA)
 mark_as_advanced(SimpleITK_USE_SYSTEM_LUA)
 if ( SimpleITK_USE_SYSTEM_LUA )
+  find_package( LuaInterp 5.1 REQUIRED )
-  find_package( LuaInterp 5.3 REQUIRED )
   set( SimpleITK_LUA_EXECUTABLE ${LUA_EXECUTABLE} CACHE PATH "Lua executable used for code generation." )
   mark_as_advanced( SimpleITK_LUA_EXECUTABLE )
   unset( LUA_EXECUTABLE CACHE )