diff --git a/Rakefile b/Rakefile
index 55f09585..00292744 100644
--- a/Rakefile
+++ b/Rakefile
@@ -258,8 +258,8 @@ task :cache_cxx_dependencies do
       cmake_flags << "-DCPM_DOWNLOAD_ALL=OFF"
       cmake_flags << "-DCPM_USE_NAMED_CACHE_DIRECTORIES=ON"
       cmake_flags << "-DCPM_USE_LOCAL_PACKAGES=OFF"
-      cmake_flags << "-DCPM_SOURCE_CACHE=\#{File.expand_path('cache', __dir__)}"
-      cmake_flags << "-DCOUCHBASE_CXX_CLIENT_EMBED_MOZILLA_CA_BUNDLE_ROOT=\#{File.expand_path('cache', __dir__)}"
+      cmake_flags << "-DCPM_SOURCE_CACHE=\#{__dir__}"
+      cmake_flags << "-DCOUCHBASE_CXX_CLIENT_EMBED_MOZILLA_CA_BUNDLE_ROOT=\#{__dir__}"
     CACHE_FLAGS
   end
 end
diff --git a/ext/extconf.rb b/ext/extconf.rb
index c57089ed..46d6b345 100644
--- a/ext/extconf.rb
+++ b/ext/extconf.rb
@@ -108,7 +108,9 @@ def sys(*cmd)
 extconf_include = File.expand_path("cache/extconf_include.rb", __dir__)
 if File.exist?(extconf_include)
   puts "-- include extra cmake options from #{extconf_include}"
-  eval(File.read(extconf_include)) # rubocop:disable Security/Eval
+  # Evaluated with the file name so that __dir__ inside the snippet resolves to the
+  # cache directory on the installing machine rather than nil.
+  eval(File.read(extconf_include), binding, extconf_include) # rubocop:disable Security/Eval
 end
 
 if ENV["CB_STATIC"] || ENV["CB_STATIC_BORINGSSL"]