diff --git a/.github/workflows/Specs.yml b/.github/workflows/Specs.yml
index 32c74e4e..ae749e52 100644
--- a/.github/workflows/Specs.yml
+++ b/.github/workflows/Specs.yml
@@ -8,7 +8,7 @@ jobs:
         os: [ubuntu-20.04]
         ruby: [2.6, 2.7, 3.0.0, 3.2.2]
         include:
-          - os: macos-11
+          - os: macos-13
             ruby: system
 
     name: ${{ matrix.os }} / Ruby ${{ matrix.ruby }}
diff --git a/lib/cocoapods-core/cdn_source.rb b/lib/cocoapods-core/cdn_source.rb
index 9345a9fe..a24cb9a0 100644
--- a/lib/cocoapods-core/cdn_source.rb
+++ b/lib/cocoapods-core/cdn_source.rb
@@ -116,7 +116,7 @@ def versions(name)
       pod_path_actual = pod_path(name)
       pod_path_relative = relative_pod_path(name)
 
-      return nil if @version_arrays_by_fragment_by_name[fragment][name].nil?
+      return nil if @version_arrays_by_fragment_by_name.dig(fragment, name).nil?
 
       concurrent_requests_catching_errors do
         loaders = []
@@ -282,14 +282,19 @@ def ensure_versions_file_loaded(fragment)
       # We use those because you can't get a directory listing from a CDN.
       index_file_name = index_file_name_for_fragment(fragment)
       download_file(index_file_name)
-      versions_raw = local_file(index_file_name, &:to_a).map(&:chomp)
-      @version_arrays_by_fragment_by_name[fragment] = versions_raw.reduce({}) do |hash, row|
-        row = row.split('/')
-        pod = row.shift
-        versions = row
-
-        hash[pod] = versions
-        hash
+      file_okay = local_file_okay?(index_file_name)
+      if file_okay
+        versions_raw = local_file(index_file_name, &:to_a).map(&:chomp)
+        @version_arrays_by_fragment_by_name[fragment] = versions_raw.reduce({}) do |hash, row|
+          row = row.split('/')
+          pod = row.shift
+          versions = row
+
+          hash[pod] = versions
+          hash
+        end
+      else
+        debug "CDN: #{name} Relative path: #{index_file_name} not available in this source set"
       end
     end
 
diff --git a/spec/cdn_source_spec.rb b/spec/cdn_source_spec.rb
index af7fe4da..b0f43496 100644
--- a/spec/cdn_source_spec.rb
+++ b/spec/cdn_source_spec.rb
@@ -424,6 +424,7 @@ def typhoeus_non_http_response_future(code)
       end
 
       it 'matches case' do
+        @source.expects(:debug).with { |cmd| cmd =~ /CDN: #{@source.name} Relative path: all_pods_versions_9_5_b\.txt not available in this source set/ }
         @source.expects(:debug).with { |cmd| cmd =~ /CDN: #{@source.name} Relative path downloaded: all_pods_versions_9_5_b\.txt, save ETag:/ }
         @source.search('bEacoNKIT').should.be.nil?
       end