diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@@ -148,10 +148,9 @@
   get_errc_messages(LLVM_LIT_ERRC_MESSAGES)
 
 #Handle unittests when out-of-tree
-#LLVM_BUILD_MAIN_SRC_DIR - Path to llvm source when out-of-tree.
   set(FLANG_GTEST_AVAIL 0)
   if (FLANG_INCLUDE_TESTS)
-    set(UNITTEST_DIR ${LLVM_BUILD_MAIN_SRC_DIR}/utils/unittest)
+    set(UNITTEST_DIR ${LLVM_THIRD_PARTY_DIR}/unittest)
     if(EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h)
       if (NOT TARGET llvm_gtest)
         add_library(llvm_gtest