diff --git a/unittests/VMCore/CMakeLists.txt b/unittests/VMCore/CMakeLists.txt
index 04eabf0b9ee..c7392a93ea2 100644
--- a/unittests/VMCore/CMakeLists.txt
+++ b/unittests/VMCore/CMakeLists.txt
@@ -22,6 +22,12 @@ if(MSVC AND MSVC_VERSION LESS 1600)
   list(REMOVE_ITEM VMCoreSources ValueMapTest.cpp)
 endif()
 
+# HACK: Declare a couple of source files as optionally compiled to satisfy the
+# missing-file-checker in LLVM's weird CMake build.
+set(LLVM_OPTIONAL_SOURCES
+  ValueMapTest.cpp
+  )
+
 add_llvm_unittest(VMCoreTests
   ${VMCoreSources}
   )