diff --git a/build/toolchain.android.mak b/build/toolchain.android.mak
index f24462a72..2249be610 100644
--- a/build/toolchain.android.mak
+++ b/build/toolchain.android.mak
@@ -9,20 +9,26 @@ endif
 
 NDK_TOOLCHAIN_PATH = $(NDK_PATH)/toolchains/llvm/prebuilt/$(NDK_HOST_TAG)/bin
 
+# No 64 bit device has ever shipped with an API level < 21. Consequently, there
+# is no toolchain for those archs on those API levels. Let's enforce NDK_VERSION
+# at 21 for these archs, and 16 for the others.
+
 ifeq ($(NDK_ABI),armeabi-v7a)
   NDK_TARGET = armv7a-linux-androideabi
+  NDK_VERSION = 16
 else ifeq ($(NDK_ABI),arm64-v8a)
   NDK_TARGET = aarch64-linux-android
+  NDK_VERSION = 21
 else ifeq ($(NDK_ABI),x86)
   NDK_TARGET = i686-linux-android
+  NDK_VERSION = 16
 else ifeq ($(NDK_ABI),x86_64)
   NDK_TARGET = x86_64-linux-android
+  NDK_VERSION = 21
 endif
 
 ifdef NDK_TARGET
 
-NDK_VERSION ?= 21
-
 CC = $(NDK_TOOLCHAIN_PATH)/$(NDK_TARGET)$(NDK_VERSION)-clang
 CXX = $(NDK_TOOLCHAIN_PATH)/$(NDK_TARGET)$(NDK_VERSION)-clang++
 LD = $(NDK_TOOLCHAIN_PATH)/$(NDK_TARGET)$(NDK_VERSION)-clang++