diff --git a/clang-tools-extra/clangd/unittests/lit.cfg.py b/clang-tools-extra/clangd/unittests/lit.cfg.py
index 48ee5f5d5ab92..33aa9e61f4ce9 100644
--- a/clang-tools-extra/clangd/unittests/lit.cfg.py
+++ b/clang-tools-extra/clangd/unittests/lit.cfg.py
@@ -1,4 +1,5 @@
 import lit.formats
+import lit.util
 
 config.name = "Clangd Unit Tests"
 config.test_format = lit.formats.GoogleTest(".", "Tests")
@@ -9,6 +10,13 @@
 # FIXME: it seems every project has a copy of this logic. Move it somewhere.
 import platform
 
+# Clangd unittests uses ~4 threads per test. So make sure we don't over commit.
+core_count = lit.util.usable_core_count()
+# FIXME: Split unittests into groups that use threads, and groups that do not,
+# and only limit multi-threaded tests.
+lit_config.parallelism_groups["clangd"] = max(1, core_count // 4)
+config.parallelism_group = "clangd"
+
 if platform.system() == "Darwin":
     shlibpath_var = "DYLD_LIBRARY_PATH"
 elif platform.system() == "Windows":