diff --git a/AppMakefile.mk b/AppMakefile.mk
index a1a0e5c84..055752c67 100644
--- a/AppMakefile.mk
+++ b/AppMakefile.mk
@@ -57,14 +57,29 @@ $(call check_no_spaces, PACKAGE_NAME)
 # Arguments:
 # - $(1): Pattern matching all arch-specific library files.
 # - $(2): The path to the library.
+# - $(3): The uppercase name of the library.
 define EXTERN_LIB_BUILD_RULE
 
 ifneq "$$(wildcard $(2)/Makefile.setup)" ""
 # Since a Makefile.setup exists, do any setup steps needed to fetch the library.
+
+ifneq "$$(wildcard $(2)/Makefile.version)" ""
+# Since a Makefile.version exists, use it to set the necessary dependency.
+include $(2)/Makefile.version
+
+$$($(3)_SENTINEL_FILE):
+	$$(MAKE) -C $(2) -f Makefile.setup all
+	$$(MAKE) -C $(2) -f Makefile all
+
+$(1): $$($(3)_SENTINEL_FILE) ;
+else
+# No Makefile.version, so this will work the first time the library is built.
 $(1):
 	$$(MAKE) -C $(2) -f Makefile.setup all
 	$$(MAKE) -C $(2) -f Makefile all
+endif
 else
+# No setup needed, just build the library the first time.
 $(1):
 	$$(MAKE) -C $(2) -f Makefile all
 endif
@@ -90,8 +105,8 @@ $$(notdir $(1))_BUILDDIR ?= $(1)/build
 $$(foreach arch, $$(TOCK_ARCHS), $$(eval LIBS_$$(arch) += $$($(notdir $(1))_BUILDDIR)/$$(arch)/$(notdir $(1)).a))
 
 # Generate rule for building the library.
-# $$(info $$(call EXTERN_LIB_BUILD_RULE,$$(foreach arch,$$(TOCK_ARCHS),%/$$(arch)/$(notdir $(1)).a),$(1)))
-$$(eval $$(call EXTERN_LIB_BUILD_RULE,$$(foreach arch,$$(TOCK_ARCHS),%/$$(arch)/$(notdir $(1)).a),$(1)))
+# $$(info $$(call EXTERN_LIB_BUILD_RULE,$$(foreach arch,$$(TOCK_ARCHS),%/$$(arch)/$(notdir $(1)).a),$(1),$(shell echo '$(notdir $(1))' | tr '[:lower:]' '[:upper:]')))
+$$(eval $$(call EXTERN_LIB_BUILD_RULE,$$(foreach arch,$$(TOCK_ARCHS),%/$$(arch)/$(notdir $(1)).a),$(1),$(shell echo '$(notdir $(1))' | tr '[:lower:]' '[:upper:]')))
 
 endef
 
diff --git a/doc/compilation.md b/doc/compilation.md
index c6ce166b3..555901217 100644
--- a/doc/compilation.md
+++ b/doc/compilation.md
@@ -122,6 +122,10 @@ a prerequisite of building the app.
 The `Makefile.setup` file should have rules to download the source for the
 library.
 
+If a library includes a `Makefile.version` with a `<LIBRARY_NAME>_SENTINEL_FILE`
+variable set, that file will be used to determine if the library needs to be
+rebuilt.
+
 **Example:** the `u8g2` library uses this.
 
 ### Pre-built libraries
diff --git a/u8g2/Makefile b/u8g2/Makefile
index 6b55615d5..fe56086cd 100644
--- a/u8g2/Makefile
+++ b/u8g2/Makefile
@@ -1,11 +1,10 @@
-# Git hash of the library to use
-VERSION_HASH := c4f9cd9f8717661c46be16bfbcb0017d785db3c1
+include Makefile.version
 
 # Base folder definitions
 TOCK_USERLAND_BASE_DIR ?= ..
 LIBNAME := u8g2
 $(LIBNAME)_DIR := $(TOCK_USERLAND_BASE_DIR)/$(LIBNAME)
-LIB_SRC_DIR := $($(LIBNAME)_DIR)/u8g2-$(VERSION_HASH)
+LIB_SRC_DIR := $($(LIBNAME)_DIR)/u8g2-$(U8G2_VERSION_HASH)
 
 # List all C and Assembly files
 $(LIBNAME)_SRCS_ALL  += $(wildcard $(LIB_SRC_DIR)/csrc/u8g2*.c)
diff --git a/u8g2/Makefile.app b/u8g2/Makefile.app
index db645d1a7..30ffa0b67 100644
--- a/u8g2/Makefile.app
+++ b/u8g2/Makefile.app
@@ -1,5 +1,5 @@
-# Git hash of the library to use. Must match the hash in Makefile.
-U8G2_VERSION_HASH := c4f9cd9f8717661c46be16bfbcb0017d785db3c1
+# Git hash of the library to use. Must match the hash in Makefile.version.
+U8G2_VERSION_HASH := bde09fbf787892c79a184e88b124aa5c79393aed
 
 # Base folder definitions
 U8G2_LIB_DIR := $(TOCK_USERLAND_BASE_DIR)/u8g2
diff --git a/u8g2/Makefile.setup b/u8g2/Makefile.setup
index f54dc709e..e276b59f0 100644
--- a/u8g2/Makefile.setup
+++ b/u8g2/Makefile.setup
@@ -2,14 +2,7 @@
 ### Helper Makefile for downloading the U8G2 library and unzipping.
 ###
 
-TOCK_USERLAND_BASE_DIR ?= ..
-
-# Git hash of the library to use. Must match the hash in Makefile.
-U8G2_VERSION_HASH := c4f9cd9f8717661c46be16bfbcb0017d785db3c1
-
-# Base folder definitions
-U8G2_LIB_DIR := $(TOCK_USERLAND_BASE_DIR)/u8g2
-U8G2_SRC_DIR := $(U8G2_LIB_DIR)/u8g2-$(U8G2_VERSION_HASH)
+include Makefile.version
 
 # Rules to download the source repository if needed. These are here so that the
 # expanded library is available before calling into the library Makefile.
@@ -17,8 +10,8 @@ $(U8G2_SRC_DIR).zip:
 	curl -L --output $(U8G2_SRC_DIR).zip https://codeload.github.com/olikraus/u8g2/zip/$(U8G2_VERSION_HASH)
 
 # The .h file will exist when the library is unzipped.
-$(U8G2_SRC_DIR)/csrc/u8g2.h: | $(U8G2_SRC_DIR).zip
+$(U8G2_SENTINEL_FILE): | $(U8G2_SRC_DIR).zip
 	unzip -q -d $(U8G2_LIB_DIR) $(U8G2_SRC_DIR).zip
 
 # Main rule to check if we need to fetch the library.
-all: | $(U8G2_SRC_DIR)/csrc/u8g2.h
+all: | $(U8G2_SENTINEL_FILE)
diff --git a/u8g2/Makefile.version b/u8g2/Makefile.version
new file mode 100644
index 000000000..ed7451b5b
--- /dev/null
+++ b/u8g2/Makefile.version
@@ -0,0 +1,15 @@
+###
+### Helper Makefile for the version of the library.
+###
+
+TOCK_USERLAND_BASE_DIR ?= ..
+
+# Git hash of the library to use. Must match the hash in Makefile.
+U8G2_VERSION_HASH := bde09fbf787892c79a184e88b124aa5c79393aed
+
+# Base folder definitions
+U8G2_LIB_DIR := $(TOCK_USERLAND_BASE_DIR)/u8g2
+U8G2_SRC_DIR := $(U8G2_LIB_DIR)/u8g2-$(U8G2_VERSION_HASH)
+
+# The file we use to determine if the library has been fetched and built.
+U8G2_SENTINEL_FILE := $(U8G2_SRC_DIR)/csrc/u8g2.h