diff --git a/android-toolchain-ndk-r19c.cmake b/android-toolchain-ndk-r21d.cmake
similarity index 91%
rename from android-toolchain-ndk-r19c.cmake
rename to android-toolchain-ndk-r21d.cmake
index 654320f7..02e4ffd4 100644
--- a/android-toolchain-ndk-r19c.cmake
+++ b/android-toolchain-ndk-r21d.cmake
@@ -36,8 +36,9 @@ endif()
 set(supported_ndks
   ndk-r19c
   ndk-r20  # compiler bugs pending, to be fixed in ndk-r21
+  ndk-r21d
 )
-set(ANDROID_TOOLCHAIN_VERSION "ndk-r19c" CACHE STRING
+set(ANDROID_TOOLCHAIN_VERSION "ndk-r21d" CACHE STRING
   "Version of the Android NDK toolchain to be used"
 )
 if(NOT ANDROID_TOOLCHAIN_VERSION IN_LIST supported_ndks)
@@ -97,12 +98,24 @@ if(CMAKE_BUILD_TYPE MATCHES Rel)
 	endif()
 endif()
 
+# Cf. https://developer.android.com/studio/command-line/variables
+if(NOT DEFINED ANDROID_SDK_ROOT AND NOT "$ENV{ANDROID_HOME}" STREQUAL "")
+	message(STATUS "Using ANDROID_SDK_ROOT=ANDROID_HOME=$ENV{ANDROID_HOME}")
+	set(ANDROID_SDK_ROOT "$ENV{ANDROID_HOME}")
+endif()
 if(NOT DEFINED ANDROID_SDK_ROOT AND NOT "$ENV{ANDROID_SDK_ROOT}" STREQUAL "")
+	message(STATUS "Using ANDROID_SDK_ROOT=$ENV{ANDROID_SDK_ROOT}")
 	set(ANDROID_SDK_ROOT "$ENV{ANDROID_SDK_ROOT}")
 endif()
+if(NOT DEFINED ANDROID_NDK_ROOT AND NOT "$ENV{ANDROID_NDK_HOME}" STREQUAL "")
+	message(STATUS "Using ANDROID_NDK_ROOT=ANDROID_NDK_HOME=$ENV{ANDROID_NDK_HOME}")
+	set(ANDROID_NDK_ROOT "$ENV{ANDROID_NDK_HOME}")
+endif()
 if(NOT DEFINED ANDROID_NDK_ROOT AND NOT "$ENV{ANDROID_NDK_ROOT}" STREQUAL "")
+	message(STATUS "Using ANDROID_NDK_ROOT=$ENV{ANDROID_NDK_ROOT}")
 	set(ANDROID_NDK_ROOT "$ENV{ANDROID_NDK_ROOT}")
 endif()
+
 if(NOT "$ENV{ANDROID_PLATFORM}" STREQUAL "")
 	foreach(abi ${supported_abis})
 		set(system_platform_${abi} "$ENV{ANDROID_PLATFORM}")
@@ -112,39 +125,40 @@ elseif(DEFINED ANDROID_PLATFORM)
 		set(system_platform_${abi} "${ANDROID_PLATFORM}")
 	endforeach()
 endif()
+
 if(NOT DEFINED ANDROID_COMPILE_SDK AND NOT "$ENV{ANDROID_COMPILE_SDK}" STREQUAL "")
 	set(ANDROID_COMPILE_SDK "$ENV{ANDROID_COMPILE_SDK}")
 else()
-	set(ANDROID_COMPILE_SDK android-28)
+	set(ANDROID_COMPILE_SDK android-29)
 endif()
 
-if(ANDROID_SDK_ROOT AND ANDROID_NDK_ROOT)
-	set(sdk_host "") # external SDK and NDK
-elseif(APPLE AND CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
-	set(sdk_host "darwin")
-elseif(UNIX AND NOT APPLE AND CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
+if(NOT CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
+	message(FATAL_ERROR "CMAKE_SYSTEM_PROCESSOR must be x86_64")
+elseif(APPLE)
+	set(sdk_host "mac")
+elseif(UNIX)
 	set(sdk_host "linux")
-elseif(NOT ANDROID_SDK_ROOT)
-	message(FATAL_ERROR "ANDROID_SDK_ROOT must be set to an external SDK")
-elseif(NOT ANDROID_NDK_ROOT)
-	message(FATAL_ERROR "ANDROID_NDK_ROOT must be set to an external NDK")
+else()
+	set(sdk_host "windows")
 endif()
 
 set(android_toolchain_dependencies )
 
 
 if(NOT ANDROID_SDK_ROOT)
-	# Download SDK tools, platform, platform tools, and build tools.
-	set(sdk_tools_version   "4333796")
-	set(sdk_tools_darwin_${sdk_tools_version}_hash SHA256=ecb29358bc0f13d7c2fa0f9290135a5b608e38434aad9bf7067d0252c160853e)
-	set(sdk_tools_linux_${sdk_tools_version}_hash  SHA256=92ffee5a1d98d856634e8b71132e8a95d96c83a63fde1099be3d86df3106def9)
-	set(build_tools_version "28.0.2")
+	# Download command line tools, platform tools, platform, and build tools.
+	set(sdk_tools_version "6609375")
+	set(sdk_tools_mac_${sdk_tools_version}_hash   SHA256=2c3822db1c916655223e5ee8ce0fbf6b73d0b99012045c9dc8eaa6a5736c0c55)
+	set(sdk_tools_linux_${sdk_tools_version}_hash SHA256=89f308315e041c93a37a79e0627c47f21d5c5edbe5e80ea8dc0aac8a649e0e92)
+	set(build_tools_version "29.0.2")
 	string(CONCAT sdk_setup_sh [[
 # Generated by ]] "${CMAKE_CURRENT_LIST_FILE}\n" [[
-echo y | ./tools/bin/sdkmanager --install "platforms;]] "${ANDROID_COMPILE_SDK}" [["
-echo y | ./tools/bin/sdkmanager --install "platform-tools"
-echo y | ./tools/bin/sdkmanager --install "build-tools;]] "${build_tools_version}" [["
-yes    | ./tools/bin/sdkmanager --licenses
+set -x
+echo y | ./cmdline-tools/tools/bin/sdkmanager --update
+echo y | ./cmdline-tools/tools/bin/sdkmanager --install "platforms;]] "${ANDROID_COMPILE_SDK}" [["
+echo y | ./cmdline-tools/tools/bin/sdkmanager --install "platform-tools"
+echo y | ./cmdline-tools/tools/bin/sdkmanager --install "build-tools;]] "${build_tools_version}" [["
+yes    | ./cmdline-tools/tools/bin/sdkmanager --licenses
 ]]
 	)
 	set(ANDROID_SDK_INSTALL_ROOT "${PROJECT_BINARY_DIR}/source" CACHE STRING
@@ -158,14 +172,14 @@ yes    | ./tools/bin/sdkmanager --licenses
 	  SOURCE_WRITE
 	    sdk_setup.sh  sdk_setup_sh
 	  SOURCE
-	    DOWNLOAD_NAME android-sdk-tools-${sdk_host}-${sdk_tools_version}.zip
-	    URL           https://dl.google.com/android/repository/sdk-tools-${sdk_host}-${sdk_tools_version}.zip
+            DOWNLOAD_NAME android-commandlinetools-${sdk_host}-${sdk_tools_version}_latest.zip
+	    URL           https://dl.google.com/android/repository/commandlinetools-${sdk_host}-${sdk_tools_version}_latest.zip
 	    URL_HASH      ${sdk_tools_${sdk_host}_${sdk_tools_version}_hash}
 	    DOWNLOAD_NO_EXTRACT 1 # We extract manually from within the source directory.
 	    PATCH_COMMAND
-	      "${CMAKE_COMMAND}" -E make_directory "${ANDROID_SDK_ROOT}"
+	      "${CMAKE_COMMAND}" -E make_directory "${ANDROID_SDK_ROOT}/cmdline-tools"
 	    COMMAND
-	      "${CMAKE_COMMAND}" -E chdir "${ANDROID_SDK_ROOT}"
+	      "${CMAKE_COMMAND}" -E chdir "${ANDROID_SDK_ROOT}/cmdline-tools"
 	        "${CMAKE_COMMAND}" -E tar xzf "<DOWNLOADED_FILE>"
 	    COMMAND
 	      "${CMAKE_COMMAND}" -E chdir "${ANDROID_SDK_ROOT}"
@@ -182,6 +196,8 @@ if(NOT ANDROID_NDK_ROOT)
 	set(ndk_r19c_linux_hash  SHA1=fd94d0be6017c6acbd193eb95e09cf4b6f61b834)
 	set(ndk_r20_darwin_hash  SHA1=96d5f1c50452596912d1982439c514194b5751e6)
 	set(ndk_r20_linux_hash   SHA1=8665fc84a1b1f0d6ab3b5fdd1e30200cc7b9adff)
+	set(ndk_r21d_darwin_hash SHA1=ef06c9f9d7efd6f243eb3c05ac440562ae29ae12)
+	set(ndk_r21d_linux_hash  SHA1=bcf4023eb8cb6976a4c7cff0a8a8f145f162bf4d)
 	set(ANDROID_NDK_INSTALL_ROOT "${PROJECT_BINARY_DIR}/source" CACHE STRING
 	  "The directory where to install the downloaded NDK (i.e. the basedir of ANDROID_NDK_ROOT)"
 	)