diff --git a/llvm/utils/benchmark/CMakeLists.txt b/llvm/utils/benchmark/CMakeLists.txt
--- a/llvm/utils/benchmark/CMakeLists.txt
+++ b/llvm/utils/benchmark/CMakeLists.txt
@@ -76,8 +76,11 @@
 
 
 # Read the git tags to determine the project version
-include(GetGitVersion)
-get_git_version(GIT_VERSION)
+# WARNING: This is meaningless for when the benchmark library is being built in-tree,
+# so disable it and hardcode a null version.
+# include(GetGitVersion)
+# get_git_version(GIT_VERSION)
+set(GIT_VERSION "v0.0.0")
 
 # Tell the user what versions we are using
 string(REGEX MATCH "[0-9]+\\.[0-9]+\\.[0-9]+" VERSION ${GIT_VERSION})
diff --git a/llvm/utils/benchmark/README.LLVM b/llvm/utils/benchmark/README.LLVM
--- a/llvm/utils/benchmark/README.LLVM
+++ b/llvm/utils/benchmark/README.LLVM
@@ -21,3 +21,5 @@
   is applied to fix building with MinGW headers for ARM
 * https://github.com/google/benchmark/commit/a9b31c51b1ee7ec7b31438c647123c2cbac5d956
   is applied to disable exceptions in Microsoft STL when exceptions are disabled
+* Disabled CMake get_git_version as it is meaningless for this in-tree build,
+  and hardcoded a null version