diff --git a/core/Makefile b/core/Makefile
index e41d09e..cdfca84 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -5,7 +5,7 @@
 LOCAL_PATH := $(BUILD_SYSTEM)
 
 # Pick a reasonable string to use to identify files.
-ifneq "" "$(filter eng.%,$(BUILD_NUMBER))"
+ifneq (,$(filter eng.%,$(BUILD_NUMBER)))
   # BUILD_NUMBER has a timestamp in it, which means that
   # it will change every time.  Pick a stable value.
   FILE_NAME_TAG := eng.$(USER)
@@ -171,7 +171,7 @@
   # release build number or branch.buld_number non-release builds
 
   # Dev. branches should have DISPLAY_BUILD_NUMBER set
-  ifeq "true" "$(DISPLAY_BUILD_NUMBER)"
+  ifeq (true,$(DISPLAY_BUILD_NUMBER))
     BUILD_DISPLAY_ID := $(BUILD_ID).$(BUILD_NUMBER_FROM_FILE) $(BUILD_KEYS)
   else
     BUILD_DISPLAY_ID := $(BUILD_ID) $(BUILD_KEYS)
diff --git a/core/cleanbuild.mk b/core/cleanbuild.mk
index 22b9664..fa89758 100644
--- a/core/cleanbuild.mk
+++ b/core/cleanbuild.mk
@@ -165,7 +165,7 @@
 PREVIOUS_BUILD_CONFIG := $(strip $(PREVIOUS_BUILD_CONFIG))
 
 ifdef PREVIOUS_BUILD_CONFIG
-  ifneq "$(current_build_config)" "$(PREVIOUS_BUILD_CONFIG)"
+  ifneq ($(current_build_config),$(PREVIOUS_BUILD_CONFIG))
     $(info *** Build configuration changed: "$(PREVIOUS_BUILD_CONFIG)" -> "$(current_build_config)")
     ifneq ($(DISABLE_AUTO_INSTALLCLEAN),true)
       force_installclean := true
@@ -272,7 +272,7 @@
 	$(hide) rm -rf $(FILES)
 	@echo "Deleted images and staging directories."
 
-ifeq "$(force_installclean)" "true"
+ifeq ($(force_installclean),true)
   $(info *** Forcing "make installclean"...)
   $(info *** rm -rf $(dataclean_files) $(installclean_files))
   $(shell rm -rf $(dataclean_files) $(installclean_files))
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 86d77bb..2245aa2 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -34,7 +34,7 @@
 # if the file exists.
 #
 INTERNAL_BUILD_ID_MAKEFILE := $(wildcard $(BUILD_SYSTEM)/build_id.mk)
-ifneq "" "$(INTERNAL_BUILD_ID_MAKEFILE)"
+ifdef INTERNAL_BUILD_ID_MAKEFILE
   include $(INTERNAL_BUILD_ID_MAKEFILE)
 endif
 
@@ -76,7 +76,7 @@
 $(foreach v,$(ENABLED_VERSIONS), \
   $(eval IS_AT_LEAST_$(v) := true))
 
-ifeq "" "$(PLATFORM_VERSION)"
+ifndef PLATFORM_VERSION
   # This is the canonical definition of the platform version,
   # which is the version that we reveal to the end user.
   # Update this value when the platform version changes (rather
@@ -84,7 +84,7 @@
   PLATFORM_VERSION := 7.1.1
 endif
 
-ifeq "" "$(PLATFORM_SDK_VERSION)"
+ifndef PLATFORM_SDK_VERSION
   # This is the canonical definition of the SDK version, which defines
   # the set of APIs and functionality available in the platform.  It
   # is a single integer that increases monotonically as updates to
@@ -96,7 +96,7 @@
   PLATFORM_SDK_VERSION := 25
 endif
 
-ifeq "" "$(PLATFORM_JACK_MIN_SDK_VERSION)"
+ifndef PLATFORM_JACK_MIN_SDK_VERSION
   # This is definition of the min SDK version given to Jack for the current
   # platform. For released version it should be the same as
   # PLATFORM_SDK_VERSION. During development, this number may be incremented
@@ -105,7 +105,7 @@
   PLATFORM_JACK_MIN_SDK_VERSION := o-b1
 endif
 
-ifeq "" "$(PLATFORM_VERSION_CODENAME)"
+ifndef PLATFORM_VERSION_CODENAME
   # This is the current development code-name, if the build is not a final
   # release build.  If this is a final release build, it is simply "REL".
   PLATFORM_VERSION_CODENAME := REL
@@ -116,10 +116,10 @@
   PLATFORM_VERSION_ALL_CODENAMES := $(PLATFORM_VERSION_CODENAME)
 endif
 
-ifeq "REL" "$(PLATFORM_VERSION_CODENAME)"
+ifeq (REL,$(PLATFORM_VERSION_CODENAME))
   PLATFORM_PREVIEW_SDK_VERSION := 0
 else
-  ifeq "" "$(PLATFORM_PREVIEW_SDK_VERSION)"
+  ifndef PLATFORM_PREVIEW_SDK_VERSION
     # This is the definition of a preview SDK version over and above the current
     # platform SDK version. Unlike the platform SDK version, a higher value
     # for preview SDK version does NOT mean that all prior preview APIs are
@@ -133,20 +133,20 @@
   endif
 endif
 
-ifeq "" "$(DEFAULT_APP_TARGET_SDK)"
+ifndef DEFAULT_APP_TARGET_SDK
   # This is the default minSdkVersion and targetSdkVersion to use for
   # all .apks created by the build system.  It can be overridden by explicitly
   # setting these in the .apk's AndroidManifest.xml.  It is either the code
   # name of the development build or, if this is a release build, the official
   # SDK version of this release.
-  ifeq "REL" "$(PLATFORM_VERSION_CODENAME)"
+  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
     DEFAULT_APP_TARGET_SDK := $(PLATFORM_SDK_VERSION)
   else
     DEFAULT_APP_TARGET_SDK := $(PLATFORM_VERSION_CODENAME)
   endif
 endif
 
-ifeq "" "$(PLATFORM_SECURITY_PATCH)"
+ifndef PLATFORM_SECURITY_PATCH
     #  Used to indicate the security patch that has been applied to the device.
     #  It must signify that the build includes all security patches issued up through the designated Android Public Security Bulletin.
     #  It must be of the form "YYYY-MM-DD" on production devices.
@@ -155,7 +155,7 @@
       PLATFORM_SECURITY_PATCH := 2016-11-05
 endif
 
-ifeq "" "$(PLATFORM_BASE_OS)"
+ifndef PLATFORM_BASE_OS
   # Used to indicate the base os applied to the device.
   # Can be an arbitrary string, but must be a single word.
   #
@@ -163,7 +163,7 @@
   PLATFORM_BASE_OS :=
 endif
 
-ifeq "" "$(BUILD_ID)"
+ifndef BUILD_ID
   # Used to signify special builds.  E.g., branches and/or releases,
   # like "M5-RC7".  Can be an arbitrary string, but must be a single
   # word and a valid file name.
@@ -172,7 +172,7 @@
   BUILD_ID := UNKNOWN
 endif
 
-ifeq "" "$(BUILD_DATETIME)"
+ifndef BUILD_DATETIME
   # Used to reproduce builds by setting the same time. Must be the number
   # of seconds since the Epoch.
   BUILD_DATETIME := $(shell date +%s)
@@ -184,7 +184,7 @@
 DATE := date -d @$(BUILD_DATETIME)
 endif
 
-ifeq "" "$(BUILD_NUMBER)"
+ifndef BUILD_NUMBER
   # BUILD_NUMBER should be set to the source control value that
   # represents the current state of the source code.  E.g., a
   # perforce changelist number or a git hash.  Can be an arbitrary string