diff --git a/CMakeLists.txt b/CMakeLists.txt
index 62e458f9b..e54bceecf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -32,13 +32,11 @@ project(openthread)
 option(OT_BUILD_EXECUTABLES "Build executables" ON)
 option(OT_BUILTIN_MBEDTLS "Enable builtin mbedTLS" ON)
 
-set(OT_ROOT_DIR ${PROJECT_SOURCE_DIR} CACHE INTERNAL "OpenThread source root.")
-
-include("${OT_ROOT_DIR}/etc/cmake/checks.cmake")
-include("${OT_ROOT_DIR}/etc/cmake/options.cmake")
+include("${PROJECT_SOURCE_DIR}/etc/cmake/checks.cmake")
+include("${PROJECT_SOURCE_DIR}/etc/cmake/options.cmake")
 
 execute_process(
-    COMMAND "${OT_ROOT_DIR}/third_party/nlbuild-autotools/repo/scripts/mkversion" "-b" "`cat .default-version`" "."
+    COMMAND "${PROJECT_SOURCE_DIR}/third_party/nlbuild-autotools/repo/scripts/mkversion" "-b" "`cat .default-version`" "."
     OUTPUT_VARIABLE __version OUTPUT_STRIP_TRAILING_WHITESPACE
 )
 set(OT_VERSION "${__version}")
@@ -52,7 +50,7 @@ set(OT_PLATFORM "none" CACHE STRING "Target platform chosen by the user at confi
 
 function(ot_get_platforms arg_platforms)
     set(result "none")
-    set(platforms_dir "${OT_ROOT_DIR}/examples/platforms")
+    set(platforms_dir "${PROJECT_SOURCE_DIR}/examples/platforms")
     file(GLOB platforms RELATIVE "${platforms_dir}" "${platforms_dir}/*")
     foreach(platform IN LISTS platforms)
         if(IS_DIRECTORY "${platforms_dir}/${platform}")
@@ -69,19 +67,19 @@ if(NOT OT_PLATFORM IN_LIST OT_EXAMPLE_PLATFORMS)
     message(FATAL_ERROR "Platform unknown: ${OT_PLATFORM}")
 endif()
 
-list(APPEND OT_PUBLIC_INCLUDES ${OT_ROOT_DIR}/etc/cmake)
-list(APPEND OT_PUBLIC_INCLUDES ${OT_ROOT_DIR}/include)
+list(APPEND OT_PUBLIC_INCLUDES ${PROJECT_SOURCE_DIR}/etc/cmake)
+list(APPEND OT_PUBLIC_INCLUDES ${PROJECT_SOURCE_DIR}/include)
 
 if(NOT OT_PLATFORM MATCHES "none")
-    list(APPEND OT_PRIVATE_INCLUDES ${OT_ROOT_DIR}/examples/platforms/${OT_PLATFORM})
-    include("${OT_ROOT_DIR}/examples/platforms/${OT_PLATFORM}/platform.cmake")
+    list(APPEND OT_PRIVATE_INCLUDES ${PROJECT_SOURCE_DIR}/examples/platforms/${OT_PLATFORM})
+    include("${PROJECT_SOURCE_DIR}/examples/platforms/${OT_PLATFORM}/platform.cmake")
 endif()
 
 list(APPEND OT_PRIVATE_DEFINES ${OT_PLATFORM_DEFINES})
 
 if(OT_BUILTIN_MBEDTLS)
-    list(APPEND OT_PRIVATE_INCLUDES ${OT_ROOT_DIR}/third_party/mbedtls)
-    list(APPEND OT_PRIVATE_INCLUDES ${OT_ROOT_DIR}/third_party/mbedtls/repo/include)
+    list(APPEND OT_PRIVATE_INCLUDES ${PROJECT_SOURCE_DIR}/third_party/mbedtls)
+    list(APPEND OT_PRIVATE_INCLUDES ${PROJECT_SOURCE_DIR}/third_party/mbedtls/repo/include)
 
     list(APPEND OT_PRIVATE_DEFINES
         "MBEDTLS_CONFIG_FILE=\"mbedtls-config.h\""
diff --git a/examples/apps/cli/CMakeLists.txt b/examples/apps/cli/CMakeLists.txt
index 9f756883f..dac2bc2b9 100644
--- a/examples/apps/cli/CMakeLists.txt
+++ b/examples/apps/cli/CMakeLists.txt
@@ -37,8 +37,8 @@ add_executable(ot-cli-mtd
 set(COMMON_INCLUDES
     ${OT_PUBLIC_INCLUDES}
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/examples/platforms
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/examples/platforms
+    ${PROJECT_SOURCE_DIR}/src/core
 )
 
 target_include_directories(ot-cli-ftd PRIVATE ${COMMON_INCLUDES})
diff --git a/examples/apps/ncp/CMakeLists.txt b/examples/apps/ncp/CMakeLists.txt
index 5ac8658ac..50278505b 100644
--- a/examples/apps/ncp/CMakeLists.txt
+++ b/examples/apps/ncp/CMakeLists.txt
@@ -41,8 +41,8 @@ add_executable(ot-rcp
 set(COMMON_INCLUDES
     ${OT_PUBLIC_INCLUDES}
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/examples/platforms
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/examples/platforms
+    ${PROJECT_SOURCE_DIR}/src/core
 )
 
 target_include_directories(ot-ncp-ftd PRIVATE ${COMMON_INCLUDES})
diff --git a/examples/platforms/cc2538/CMakeLists.txt b/examples/platforms/cc2538/CMakeLists.txt
index 27cf447ed..9b928c037 100644
--- a/examples/platforms/cc2538/CMakeLists.txt
+++ b/examples/platforms/cc2538/CMakeLists.txt
@@ -47,6 +47,6 @@ target_compile_definitions(openthread-cc2538 PUBLIC ${OT_PLATFORM_DEFINES})
 target_include_directories(openthread-cc2538 PRIVATE
     ${OT_PUBLIC_INCLUDES}
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/examples/platforms
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/examples/platforms
+    ${PROJECT_SOURCE_DIR}/src/core
 )
diff --git a/examples/platforms/posix/CMakeLists.txt b/examples/platforms/posix/CMakeLists.txt
index 55f933323..76bad0e1f 100644
--- a/examples/platforms/posix/CMakeLists.txt
+++ b/examples/platforms/posix/CMakeLists.txt
@@ -55,6 +55,6 @@ target_compile_definitions(openthread-posix PUBLIC ${OT_PLATFORM_DEFINES})
 target_include_directories(openthread-posix PRIVATE
     ${OT_PUBLIC_INCLUDES}
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/examples/platforms
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/examples/platforms
+    ${PROJECT_SOURCE_DIR}/src/core
 )
diff --git a/examples/platforms/utils/CMakeLists.txt b/examples/platforms/utils/CMakeLists.txt
index 2adb8525c..0526e3745 100644
--- a/examples/platforms/utils/CMakeLists.txt
+++ b/examples/platforms/utils/CMakeLists.txt
@@ -42,10 +42,10 @@ target_compile_definitions(openthread-platform-utils PRIVATE
 target_include_directories(openthread-platform-utils PRIVATE
     ${OT_PUBLIC_INCLUDES}
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/examples/platforms
-    ${OT_ROOT_DIR}/examples/platforms/utils
-    ${OT_ROOT_DIR}/src/core
-    ${OT_ROOT_DIR}/third_party/jlink/SEGGER_RTT_V640/RTT
+    ${PROJECT_SOURCE_DIR}/examples/platforms
+    ${PROJECT_SOURCE_DIR}/examples/platforms/utils
+    ${PROJECT_SOURCE_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/third_party/jlink/SEGGER_RTT_V640/RTT
 )
 
 # Provide a static library implementation of platform-utils for non-cmake platforms
diff --git a/src/cli/CMakeLists.txt b/src/cli/CMakeLists.txt
index 765312a9d..33c9d9ec5 100644
--- a/src/cli/CMakeLists.txt
+++ b/src/cli/CMakeLists.txt
@@ -41,8 +41,8 @@ target_compile_definitions(openthread-cli-mtd PRIVATE
 
 set(COMMON_INCLUDES
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/src
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/src
+    ${PROJECT_SOURCE_DIR}/src/core
 )
 
 set(COMMON_SOURCES
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index cc5634ec4..99c58cdea 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -47,7 +47,7 @@ target_compile_definitions(openthread-radio PRIVATE
 
 set(COMMON_INCLUDES
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/src/core
 )
 
 set(COMMON_SOURCES
diff --git a/src/ncp/CMakeLists.txt b/src/ncp/CMakeLists.txt
index 3b05b8e3a..e45ffb040 100644
--- a/src/ncp/CMakeLists.txt
+++ b/src/ncp/CMakeLists.txt
@@ -50,8 +50,8 @@ target_compile_definitions(openthread-rcp PRIVATE
 
 set(COMMON_INCLUDES
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/src
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/src
+    ${PROJECT_SOURCE_DIR}/src/core
 )
 
 set(COMMON_SOURCES
diff --git a/third_party/mbedtls/CMakeLists.txt b/third_party/mbedtls/CMakeLists.txt
index 026145441..00ca41610 100644
--- a/third_party/mbedtls/CMakeLists.txt
+++ b/third_party/mbedtls/CMakeLists.txt
@@ -35,7 +35,7 @@ target_compile_definitions(mbedcrypto PRIVATE
 target_include_directories(mbedcrypto PRIVATE
     ${OT_PUBLIC_INCLUDES}
     ${OT_PRIVATE_INCLUDES}
-    ${OT_ROOT_DIR}/src/core
+    ${PROJECT_SOURCE_DIR}/src/core
 )
 
 target_sources(mbedcrypto PRIVATE