diff --git a/Makefile b/Makefile
index f3034bac3a2664b01122ea7a4b193f9b7d0afbf8..5fa37a432238eba44bbbd8446445218cf1a4bc79 100644
--- a/Makefile
+++ b/Makefile
@@ -36,11 +36,11 @@ ifneq ($(GLUON_BRANCH),)
 endif
 
 ifneq ($(GLUON_FEATURES)$(GLUON_FEATURES_standard)$(GLUON_FEATURES_tiny),)
-  $(error *** Warning: GLUON_FEATURES has been obsolete, please use the image-customization file instead.)
+  $(error *** Warning: GLUON_FEATURES has been obsolete, please use the image-customization.lua file instead.)
 endif
 
 ifneq ($(GLUON_SITE_PACKAGES)$(GLUON_SITE_PACKAGES_standard)$(GLUON_SITE_PACKAGES_tiny),)
-  $(error *** Warning: GLUON_SITE_PACKAGES has been obsolete, please use the image-customization file instead.)
+  $(error *** Warning: GLUON_SITE_PACKAGES has been obsolete, please use the image-customization.lua file instead.)
 endif
 
 GLUON_AUTOUPDATER_ENABLED ?= 0
diff --git a/contrib/ci/minimal-site/image-customization b/contrib/ci/minimal-site/image-customization.lua
similarity index 100%
rename from contrib/ci/minimal-site/image-customization
rename to contrib/ci/minimal-site/image-customization.lua
diff --git a/contrib/ci/olsr-site/image-customization b/contrib/ci/olsr-site/image-customization.lua
similarity index 100%
rename from contrib/ci/olsr-site/image-customization
rename to contrib/ci/olsr-site/image-customization.lua
diff --git a/docs/dev/packages.rst b/docs/dev/packages.rst
index 656f63019ffca643e71000ac023827e9f21b56c4..286a3014ac2bf447a546f78b8bdc82a207472366 100644
--- a/docs/dev/packages.rst
+++ b/docs/dev/packages.rst
@@ -154,7 +154,7 @@ Feature flags
 
 Feature flags provide a convenient way to define package selections without
 making it necessary to list each package explicitly. The list of features to
-enable for a Gluon build is determined by the evaluated image-customization file
+enable for a Gluon build is determined by the evaluated image-customization.lua file
 in the root-directory of the Site repository.
 
 The main feature flag definition file is ``package/features``, but each package
@@ -208,7 +208,7 @@ Example::
 This will
 
 * disable the inclusion of the (non-existent) packages *gluon-web-wizard* and *gluon-no-radvd* when their
-  corresponding feature flags are evaluated as selected in the image-customization file
+  corresponding feature flags are evaluated as selected in the image-customization.lua file
 * enable four additional config mode packages when the *web-wizard* feature is enabled
 * enable *gluon-config-mode-mesh-vpn* when both *web-wizard* and one
   of *mesh-vpn-fastd* and *mesh-vpn-tunneldigger* are enabled
diff --git a/docs/features/multidomain.rst b/docs/features/multidomain.rst
index a0dc4020a42325a9fd96383609525c8f9151bc48..853949fabfd78a4d2a62b22b2c4f50f467e60a5f 100644
--- a/docs/features/multidomain.rst
+++ b/docs/features/multidomain.rst
@@ -106,7 +106,7 @@ Via config mode
 ^^^^^^^^^^^^^^^
 
 To allow switching the domain via config mode, add ``config-mode-domain-select``
-to the enabled features in the image-customization file.
+to the enabled features in the image-customization.lua file.
 
 |image0|
 
diff --git a/docs/multidomain-site-example/image-customization b/docs/multidomain-site-example/image-customization.lua
similarity index 100%
rename from docs/multidomain-site-example/image-customization
rename to docs/multidomain-site-example/image-customization.lua
diff --git a/docs/site-example/image-customization b/docs/site-example/image-customization.lua
similarity index 100%
rename from docs/site-example/image-customization
rename to docs/site-example/image-customization.lua
diff --git a/docs/user/site.rst b/docs/user/site.rst
index ff880fe29ef7736ec8241040c7b48b17fd8beb05..b4659cc814f86d6a9ad64231420a5989357aeb2d 100644
--- a/docs/user/site.rst
+++ b/docs/user/site.rst
@@ -647,7 +647,7 @@ leading to entangled package names like *gluon-mesh-vpn-fastd-respondd* or
 *gluon-status-page-mesh-batman-adv-i18n-de*.
 
 For this reason, we have introduced *feature flags*, which can be specified
-in the using the image-customization framework. These flags allow to specify
+in the using the image-customization.lua framework. These flags allow to specify
 a set of features on a higher level than individual package names.
 
 Most Gluon packages can simply be specified as feature flags by removing the ``gluon-``
@@ -671,7 +671,7 @@ To some extent, it will even allow us to further modularize existing Gluon packa
 without necessitating changes to existing site configurations.
 
 It is still possible to override such automatic rules by removing them using 
-*packages* in the image-customization file
+*packages* in the image-customization.lua file
 (e.g., ``features { '-gluon-status-page-mesh-batman-adv' }`` to remove
 the automatically added package *gluon-status-page-mesh-batman-adv*).
 
diff --git a/scripts/image_customization_lib.lua b/scripts/image_customization_lib.lua
index 64fc1aac8cb9f12fa5ab7b98409341cbadf926bd..51ee70ae465954f6b3eaa5db257d9cc2feb4cd0f 100644
--- a/scripts/image_customization_lib.lua
+++ b/scripts/image_customization_lib.lua
@@ -10,7 +10,7 @@ local function file_exists(file)
 end
 
 local function get_customization_file_name(env)
-	return env.GLUON_SITEDIR .. '/image-customization'
+	return env.GLUON_SITEDIR .. '/image-customization.lua'
 end
 
 local function evaluate_device(env, dev)
diff --git a/scripts/target_config_lib.lua b/scripts/target_config_lib.lua
index f83d1bcc7ad8207f06e2ef1fa3efed6bba385fbd..fc06f23e6430dfaa7b59c64c8c6e992c5aca3f87 100644
--- a/scripts/target_config_lib.lua
+++ b/scripts/target_config_lib.lua
@@ -92,7 +92,7 @@ local function site_specific_packages(dev_info)
 	local feature_inherited_pkgs
 	local site_features
 
-	-- Get all enabled selections from image-customization
+	-- Get all enabled selections from image-customization.lua
 	site_selections = image_customization_lib.get_selections(env, dev_info)
 
 	-- First read enabled features from site
diff --git a/scripts/target_lib.lua b/scripts/target_lib.lua
index 0579d620d3f59e1edf0c43dd8aa73b7171587d82..5d8b645ad1895579497da6eeccf26463dc5c3bc1 100644
--- a/scripts/target_lib.lua
+++ b/scripts/target_lib.lua
@@ -78,7 +78,7 @@ end
 local function want_device(device_info)
 	local overrides = get_device_overrides(device_info)
 
-	-- Check if device is disabled via image-customization in site
+	-- Check if device is disabled via image-customization.lua in site
 	if overrides['disabled'] then
 		return false
 	end