diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index 81d4042cd3a2..be76724a66d0 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -416,13 +416,16 @@ if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)
   endif()
 endif()
 
-set(LIBCXXABI_HAS_UNDEFINED_SYMBOLS ((NOT LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS)
-    OR (LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY AND LIBCXXABI_ENABLE_SHARED)))
+set(LIBCXXABI_HAS_UNDEFINED_SYMBOLS OFF)
+if ((NOT LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS)
+    OR (LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY AND LIBCXXABI_ENABLE_SHARED))
+  set(LIBCXXABI_HAS_UNDEFINED_SYMBOLS ON)
+endif()
 
 if (LIBCXXABI_HAS_UNDEFINED_SYMBOLS)
   # Need to allow unresolved symbols if this is to work with shared library builds
   if (APPLE)
-    add_link_flags("-undefined dynamic_lookup")
+    list(APPEND LIBCXXABI_LINK_FLAGS "-undefined dynamic_lookup")
   else()
     # Relax this restriction from HandleLLVMOptions
     string(REPLACE "-Wl,-z,defs" "" CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS}")