diff --git a/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/configuration/InternationalizationConfiguration.java b/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/configuration/InternationalizationConfiguration.java
index 0064433fa..3dd0d131d 100644
--- a/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/configuration/InternationalizationConfiguration.java
+++ b/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/configuration/InternationalizationConfiguration.java
@@ -6,12 +6,20 @@
 import org.springframework.web.servlet.LocaleResolver;
 import org.springframework.web.servlet.i18n.SessionLocaleResolver;
 
+import java.util.Locale;
+
 @Configuration
 public class InternationalizationConfiguration {
     @Bean
     public LocaleResolver localeResolver() {
         // TODO if we want to control the order, we can implement our own locale resolver instead of using the SessionLocaleResolver.
         SessionLocaleResolver sessionLocaleResolver = new SessionLocaleResolver();
+
+        // NOTE: If we set a default here, Locale.getDefault's behavior will be consistent, but then Accept-Language
+        // is not honored (only ?lang=). If we do not set a default, the default is determined at runtime by the JVM.
+        // This may break unit tests if the system does not determine the default to be English.
+        // sessionLocaleResolver.setDefaultLocale(new Locale("en"));
+
         return sessionLocaleResolver;
     }
 
@@ -19,8 +27,9 @@ public LocaleResolver localeResolver() {
     public MappedResourceBundleMessageSource messageSource() {
         MappedResourceBundleMessageSource source = new MappedResourceBundleMessageSource();
         source.setBasenames("i18n/messages");
-        source.setUseCodeAsDefaultMessage(true);
-        source.setFallbackToSystemLocale(false);
+        source.setUseCodeAsDefaultMessage(false); //TODO Why was this true?
+        source.setFallbackToSystemLocale(false); // allows us to return messages.properties instead of
+                                                 // messages_en.properties for unsupported languages.
         return source;
     }
 }
diff --git a/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesController.java b/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesController.java
index c5ec89f6c..b02c0df6d 100644
--- a/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesController.java
+++ b/backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesController.java
@@ -7,6 +7,7 @@
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 
+import javax.servlet.http.HttpServletRequest;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Locale;
diff --git a/backend/src/test/groovy/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesControllerTests.groovy b/backend/src/test/groovy/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesControllerTests.groovy
index 722b929c8..9287ff552 100644
--- a/backend/src/test/groovy/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesControllerTests.groovy
+++ b/backend/src/test/groovy/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesControllerTests.groovy
@@ -106,13 +106,23 @@ class InternationalizationMessagesControllerTests extends Specification {
         result.andExpect(content().json(expectedFrenchResult))
     }
 
-    def "GET messages with an unsupported Accept-Language returns the default language"() {
+    def "GET messages with an unsupported Accept-Language returns the default (unspecified) language"() {
         when:
         def result = mockMvc.perform(
                 get(messagesUrl)
-                        .header("Accept-Language", "ja_JP"))
+                        .header("Accept-Language", "ja"))
 
         then:
-        result.andExpect(content().json(expectedEnglishResult))
+        result.andExpect(content().json(expectedDefaultResult))
+    }
+
+    def "GET messages with a made-up Accept-Language returns the default (unspecified) language"() {
+        when:
+        def result = mockMvc.perform(
+                get(messagesUrl)
+                        .header("Accept-Language", "foo"))
+
+        then:
+        result.andExpect(content().json(expectedDefaultResult))
     }
 }