diff --git a/lib/omnibus/fetchers/net_fetcher.rb b/lib/omnibus/fetchers/net_fetcher.rb
index eec94dcd3..a892bb30b 100644
--- a/lib/omnibus/fetchers/net_fetcher.rb
+++ b/lib/omnibus/fetchers/net_fetcher.rb
@@ -148,7 +148,8 @@ def download_url
       if Config.use_s3_caching
         S3Cache.url_for(self)
       elsif Config.use_internal_sources && !source[:internal]
-        raise InternalSourceMissing.new(self)
+        log.warn(log_key) { "Internal source missing for #{name}; falling back to external source URL." }
+        source[:url]
       else
         source[:url]
       end
@@ -161,6 +162,22 @@ def download_url
     #
     # @return [void]
     #
+    # def download
+    #   log.warn(log_key) { source[:warning] } if source.key?(:warning)
+
+    #   options = {}
+
+    #   if source[:unsafe]
+    #     log.warn(log_key) { "Permitting unsafe redirects!" }
+    #     options[:allow_unsafe_redirects] = true
+    #   end
+
+    #   # Set the cookie if one was given
+    #   options["Cookie"] = source[:cookie] if source[:cookie]
+    #   options["Authorization"] = source[:authorization] if source[:authorization]
+
+    #   download_file!(download_url, downloaded_file, options)
+    # end
     def download
       log.warn(log_key) { source[:warning] } if source.key?(:warning)
 
@@ -175,7 +192,19 @@ def download
       options["Cookie"] = source[:cookie] if source[:cookie]
       options["Authorization"] = source[:authorization] if source[:authorization]
 
-      download_file!(download_url, downloaded_file, options)
+      begin
+        # Attempt download from internal or S3 source URL
+        download_file!(download_url, downloaded_file, options)
+      rescue OpenURI::HTTPError => e
+        # If 404 comes from internal source, fallback to external URL
+        if e.io.status[0] == "404" && Config.use_internal_sources && source[:internal]
+          log.warn(log_key) { "Internal source returned 404 Not Found for #{name}, falling back to external source URL." }
+          download_file!(source[:url], downloaded_file, options)
+        else
+          # Re-raise other errors
+          raise
+        end
+      end
     end
 
     #
diff --git a/spec/functional/fetchers/net_fetcher_spec.rb b/spec/functional/fetchers/net_fetcher_spec.rb
index 73c278275..9215e879c 100644
--- a/spec/functional/fetchers/net_fetcher_spec.rb
+++ b/spec/functional/fetchers/net_fetcher_spec.rb
@@ -173,11 +173,15 @@ def stub_ohai(options = {}, &block); end
         end
       end
 
-      context "when use_internal_sources is true and no internal source url" do
-        before { Omnibus::Config.use_internal_sources(true) }
+      context "when use_internal_sources is true but internal source is missing" do
+        before do
+          Config.use_internal_sources(true)
+        end
 
-        it "raises an exception" do
-          expect { fetch! }.to raise_error(InternalSourceMissing)
+        it "logs a warning and falls back to the external url" do
+          expect(subject).to receive(:log).and_call_original
+          url = subject.send(:download_url)
+          expect(url).to eq(source[:url])
         end
       end