diff --git a/lib/statsd_middleware.rb b/lib/statsd_middleware.rb
index e02d7d1a1cf..4ac72528d91 100644
--- a/lib/statsd_middleware.rb
+++ b/lib/statsd_middleware.rb
@@ -52,6 +52,7 @@ class StatsdMiddleware
     veteran-id-card
     veteran-representative
     vic-v2
+    undefined
   ].freeze
 
   def initialize(app)
@@ -94,14 +95,14 @@ def call(env)
   def get_source_app(env)
     source_app = env['HTTP_SOURCE_APP_NAME']
 
-    return nil if source_app.nil?
+    return 'not_provided' if source_app.nil?
     return source_app if SOURCE_APP_NAMES.include?(source_app)
 
     # TODO: - Use sentry to notify us instead. It must be done in a rate-limited way
     #        so as not to allow for a malicious client to overflow worker queues
     Rails.logger.warn "Unrecognized value for HTTP_SOURCE_APP_NAME request header... [#{source_app}]"
 
-    ''
+    'not_in_whitelist'
   end
 
   def instrument_statsd(status, duration, controller, action, source_app)
diff --git a/spec/request/statsd_middleware_spec.rb b/spec/request/statsd_middleware_spec.rb
index 41cde81cf7a..095868de179 100644
--- a/spec/request/statsd_middleware_spec.rb
+++ b/spec/request/statsd_middleware_spec.rb
@@ -32,7 +32,7 @@
 
   it 'sends status data to statsd' do
     stub_varx_request(:get, 'mhv-api/patient/v1/prescription/gethistoryrx', history_rxs, status_code: 200)
-    tags = %w[controller:v0/prescriptions action:index source_app: status:200]
+    tags = %w[controller:v0/prescriptions action:index source_app:not_provided status:200]
     expect do
       get '/v0/prescriptions'
     end.to trigger_statsd_increment(StatsdMiddleware::STATUS_KEY, tags: tags, times: 1, value: 1)
@@ -40,7 +40,7 @@
 
   it 'sends duration data to statsd' do
     stub_varx_request(:get, 'mhv-api/patient/v1/prescription/gethistoryrx', history_rxs, status_code: 200)
-    tags = %w[controller:v0/prescriptions action:index source_app:]
+    tags = %w[controller:v0/prescriptions action:index source_app:not_provided]
     expect do
       get '/v0/prescriptions'
     end.to trigger_statsd_measure(StatsdMiddleware::DURATION_KEY, tags: tags, times: 1, value: 0.0)
@@ -63,14 +63,14 @@
   end
 
   it 'handles a missing route correctly' do
-    tags = %w[controller:application action:routing_error source_app: status:404]
+    tags = %w[controller:application action:routing_error source_app:not_provided status:404]
     expect do
       get '/v0/blahblah'
     end.to trigger_statsd_increment(StatsdMiddleware::STATUS_KEY, tags: tags, times: 1, value: 1)
   end
 
   it 'provides duration for missing routes' do
-    tags = %w[controller:application action:routing_error source_app:]
+    tags = %w[controller:application action:routing_error source_app:not_provided]
     expect do
       get '/v0/blahblah'
     end.to trigger_statsd_measure(StatsdMiddleware::DURATION_KEY, tags: tags, times: 1, value: 0.0)
@@ -84,9 +84,17 @@
     end.to trigger_statsd_increment(StatsdMiddleware::STATUS_KEY, tags: tags, times: 1)
   end
 
-  it 'uses a blank string for source_app when the value is not in white list' do
+  it 'sends undefined to statsd when source_app is undefined' do
     stub_varx_request(:get, 'mhv-api/patient/v1/prescription/gethistoryrx', history_rxs, status_code: 200)
-    tags = %w[controller:v0/prescriptions action:index source_app: status:200]
+    tags = %w[controller:v0/prescriptions action:index source_app:undefined status:200]
+    expect do
+      get '/v0/prescriptions', headers: { 'Source-App-Name' => 'undefined' }
+    end.to trigger_statsd_increment(StatsdMiddleware::STATUS_KEY, tags: tags, times: 1)
+  end
+
+  it 'uses not_in_whitelist for source_app when the value is not in white list' do
+    stub_varx_request(:get, 'mhv-api/patient/v1/prescription/gethistoryrx', history_rxs, status_code: 200)
+    tags = %w[controller:v0/prescriptions action:index source_app:not_in_whitelist status:200]
     expect do
       get '/v0/prescriptions', headers: { 'Source-App-Name' => 'foo' }
     end.to trigger_statsd_increment(StatsdMiddleware::STATUS_KEY, tags: tags, times: 1)