diff --git a/config/checkstyle/checkstyle.xml b/config/checkstyle/checkstyle.xml
index 5e8d60967..0e8a824b5 100644
--- a/config/checkstyle/checkstyle.xml
+++ b/config/checkstyle/checkstyle.xml
@@ -25,6 +25,53 @@ by Joshua Bloch in his book Effective Java -->
     <property name="message" value='TODO is preferred to FIXME.  e.g. "TODO(johndoe): Refactor when v2 is released."' />
   </module>
 
+  <!-- Checks that String.toUpper/LowerCase() is never used without locale. -->
+  <module name="RegexpSingleline">
+    <property name="format" value="\.to(Upper|Lower)Case\(\)"/>
+    <property name="message" value="String.toUpper/LowerCase() can have unexpected results depending on locale. Either set the locale explicitly - e.g., toUpperCase(Locale.ENGLISH) - or use Ascii.toUpper/LowerCase(...) instead." />
+  </module>
+
+  <!-- Checks that DateTime.now(...) is always passed a DateTimeZone parameter. -->
+  <module name="RegexpSingleline">
+    <property name="format" value="DateTime\.now\(\)"/>
+    <property name="message" value="DateTime.now() must be called with a DateTimeZone parameter, e.g. DateTime.now(UTC)" />
+  </module>
+
+  <!-- Checks that Javadoc does not include a malformed @see tag. -->
+  <module name="RegexpSingleline">
+    <property name="format" value='@see\s\"http(|s)://'/>
+    <property name="message" value='Your Javadocs appear to use invalid &lt;a&gt; tag syntax in @see tags. Please use the correct syntax: @see &lt;a href="http(s)://your_url"&gt;url_description&lt;/a&gt;'/>
+  </module>
+
+  <!-- Checks that our Ofy wrapper is used instead of the "real" ofy(). -->
+  <module name="RegexpSingleline">
+    <property name="format" value="com\.googlecode\.objectify\.ObjectifyService\.ofy"/>
+    <property name="message" value="Use google.registry.model.ofy.ObjectifyService.ofy(). Do not use com.googlecode.objectify.v4.ObjectifyService.ofy()."/>
+  </module>
+
+  <!-- Checks that java.util.Optional is used instead of Guava's Optional. -->
+  <module name="RegexpSingleline">
+    <property name="format" value="com\.google\.common\.base\.Optional"/>
+    <property name="message" value="Use java.util.Optional instead of Guava's Optional."/>
+  </module>
+
+  <!-- Checks that our backport JUnit exception assertion methods are used instead of the ones slated for release in JUnit 4.13. -->
+  <module name="RegexpSingleline">
+    <property name="format" value="org\.junit\.Assert\.(assert|expect)Throws"/>
+    <property name="message" value="Use the exception assertion methods in google.registry.testing.JUnitBackports instead of those in JUnit."/>
+  </module>
+
+  <!-- Checks that the deprecated ExpectedException is not used. -->
+  <module name="RegexpSingleline">
+    <property name="format" value="org\.junit\.rules\.ExpectedException"/>
+    <property name="message" value="Use assertThrows and expectThrows from JUnitBackports instead of the deprecated methods on ExpectedException."/>
+  </module>
+
+  <!-- Checks that the deprecated MockitoJUnitRunner is not used. -->
+  <module name="RegexpSingleline">
+    <property name="format" value="MockitoJUnitRunner"/>
+    <property name="message" value="MockitoJUnitRunner is deprecated. Use @RunWith(JUnit4.class) and MockitoRule instead."/>
+  </module>
 
   <!-- All Java AST specific tests live under TreeWalker module. -->
   <module name="TreeWalker">
diff --git a/config/checkstyle/suppressions.xml b/config/checkstyle/suppressions.xml
index cd993cc2e..405e27ab5 100644
--- a/config/checkstyle/suppressions.xml
+++ b/config/checkstyle/suppressions.xml
@@ -9,4 +9,6 @@
   <suppress files="[/\\].*[/\\]generated.*[/\\]" checks="."/>
   <!-- Ignore Javadoc checks in test files -->
   <suppress files="[/\\].*[/\\]src/test/java/.*[/\\]" checks="JavadocType"/>
+  <!-- ofy() regex check doesn't apply to these files -->
+  <suppress files="AugmentedDeleter.java|AugmentedSaver.java|Ofy.java" checks="RegexpSingleline"/>
 </suppressions>
diff --git a/core/src/main/java/google/registry/model/domain/DomainBase.java b/core/src/main/java/google/registry/model/domain/DomainBase.java
index 6f5087564..5180ca32a 100644
--- a/core/src/main/java/google/registry/model/domain/DomainBase.java
+++ b/core/src/main/java/google/registry/model/domain/DomainBase.java
@@ -104,7 +104,7 @@ public class DomainBase extends EppResource
    * from (creationTime, deletionTime) there can only be one domain in Datastore with this name.
    * However, there can be many domains with the same name and non-overlapping lifetimes.
    *
-   * @invariant fullyQualifiedDomainName == fullyQualifiedDomainName.toLowerCase()
+   * @invariant fullyQualifiedDomainName == fullyQualifiedDomainName.toLowerCase(Locale.ENGLISH)
    */
   @Index
   String fullyQualifiedDomainName;