diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -302,7 +302,9 @@
 
 # Disable DLL annotations on Windows for static builds.
 if (WIN32 AND LIBCXXABI_ENABLE_STATIC AND NOT LIBCXXABI_ENABLE_SHARED)
-  if (LIBCXX_ENABLE_SHARED AND LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+  # If LIBCXX_ENABLE_SHARED isn't set (by the user on the cmake command
+  # line or via a cache file), use its expected default value (enabled).
+  if ((LIBCXX_ENABLE_SHARED OR NOT DEFINED LIBCXX_ENABLE_SHARED) AND LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
     # Building libcxxabi statically, but intending for it to be statically
     # linked into a shared libcxx; keep dllexport enabled within libcxxabi,
     # as the symbols will need to be exported from libcxx.