diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
index c722d3416a0845..f6b1f1a2ee0404 100644
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@@ -639,6 +639,12 @@ elseif (SANITIZER_TEST_CXX_LIBNAME STREQUAL "libstdc++")
 endif()
 
 # Unittests support.
+# FIXME: When compiler-rt is build using -DLLVM_BUILD_EXTERNAL_COMPILER_RT=ON, then
+# The LLVM_THIRD_PARTY_DIR variable is not set.
+if (NOT LLVM_THIRD_PARTY_DIR)
+  set(LLVM_THIRD_PARTY_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../third-party")
+endif()
+
 set(COMPILER_RT_GTEST_PATH ${LLVM_THIRD_PARTY_DIR}/unittest/googletest)
 set(COMPILER_RT_GTEST_SOURCE ${COMPILER_RT_GTEST_PATH}/src/gtest-all.cc)
 set(COMPILER_RT_GTEST_CFLAGS