diff --git a/src/com/fsck/k9/activity/setup/Prefs.java b/src/com/fsck/k9/activity/setup/Prefs.java
index dfbec1167..fc091b1f5 100644
--- a/src/com/fsck/k9/activity/setup/Prefs.java
+++ b/src/com/fsck/k9/activity/setup/Prefs.java
@@ -5,6 +5,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import android.content.Context;
 import android.content.Intent;
@@ -168,7 +169,7 @@ public class Prefs extends K9PreferenceActivity {
         List<CharSequence> entryVector = new ArrayList<CharSequence>(Arrays.asList(mLanguage.getEntries()));
         List<CharSequence> entryValueVector = new ArrayList<CharSequence>(Arrays.asList(mLanguage.getEntryValues()));
         String supportedLanguages[] = getResources().getStringArray(R.array.supported_languages);
-        HashSet<String> supportedLanguageSet = new HashSet<String>(Arrays.asList(supportedLanguages));
+        Set<String> supportedLanguageSet = new HashSet<String>(Arrays.asList(supportedLanguages));
         for (int i = entryVector.size() - 1; i > -1; --i) {
             if (!supportedLanguageSet.contains(entryValueVector.get(i))) {
                 entryVector.remove(i);
diff --git a/src/com/fsck/k9/controller/MessagingController.java b/src/com/fsck/k9/controller/MessagingController.java
index 558a6a12a..63d2afa63 100644
--- a/src/com/fsck/k9/controller/MessagingController.java
+++ b/src/com/fsck/k9/controller/MessagingController.java
@@ -616,11 +616,11 @@ public class MessagingController implements Runnable {
                     List <? extends Folder > remoteFolders = store.getPersonalNamespaces(false);
 
                     LocalStore localStore = account.getLocalStore();
-                    HashSet<String> remoteFolderNames = new HashSet<String>();
+                    Set<String> remoteFolderNames = new HashSet<String>();
                     List<LocalFolder> foldersToCreate = new LinkedList<LocalFolder>();
 
                     localFolders = localStore.getPersonalNamespaces(false);
-                    HashSet<String> localFolderNames = new HashSet<String>();
+                    Set<String> localFolderNames = new HashSet<String>();
                     for (Folder localFolder : localFolders) {
                         localFolderNames.add(localFolder.getName());
                     }
@@ -693,7 +693,7 @@ public class MessagingController implements Runnable {
 
     public void searchLocalMessagesSynchronous(final LocalSearch search, final MessagingListener listener) {
         final AccountStats stats = new AccountStats();
-        final HashSet<String> uuidSet = new HashSet<String>(Arrays.asList(search.getAccountUuids()));
+        final Set<String> uuidSet = new HashSet<String>(Arrays.asList(search.getAccountUuids()));
         Account[] accounts = Preferences.getPreferences(mApplication.getApplicationContext()).getAccounts();
         boolean allAccounts = uuidSet.contains(SearchSpecification.ALL_ACCOUNTS);
 
diff --git a/src/com/fsck/k9/mail/Message.java b/src/com/fsck/k9/mail/Message.java
index 70ee13f30..69d65e763 100644
--- a/src/com/fsck/k9/mail/Message.java
+++ b/src/com/fsck/k9/mail/Message.java
@@ -26,7 +26,7 @@ public abstract class Message implements Part, CompositeBody {
 
     protected String mUid;
 
-    protected HashSet<Flag> mFlags = new HashSet<Flag>();
+    protected Set<Flag> mFlags = new HashSet<Flag>();
 
     protected Date mInternalDate;
 
diff --git a/src/com/fsck/k9/mail/store/ImapStore.java b/src/com/fsck/k9/mail/store/ImapStore.java
index 2c2bb2fef..87a0c2fb4 100644
--- a/src/com/fsck/k9/mail/store/ImapStore.java
+++ b/src/com/fsck/k9/mail/store/ImapStore.java
@@ -531,7 +531,7 @@ public class ImapStore extends Store {
                 return allFolders;
             } else {
                 List<Folder> resultFolders = new LinkedList<Folder>();
-                HashSet<String> subscribedFolderNames = new HashSet<String>();
+                Set<String> subscribedFolderNames = new HashSet<String>();
                 List <? extends Folder > subscribedFolders = listFolders(connection, true);
                 for (Folder subscribedFolder : subscribedFolders) {
                     subscribedFolderNames.add(subscribedFolder.getName());
@@ -1488,7 +1488,7 @@ public class ImapStore extends Store {
              * Envelope - UID FETCH ([FLAGS] INTERNALDATE UID RFC822.SIZE FLAGS BODY.PEEK[HEADER.FIELDS (date subject from content-type to cc)])
              *
              */
-            LinkedHashSet<String> fetchFields = new LinkedHashSet<String>();
+            Set<String> fetchFields = new LinkedHashSet<String>();
             fetchFields.add("UID");
             if (fp.contains(FetchProfile.Item.FLAGS)) {
                 fetchFields.add("FLAGS");
diff --git a/src/com/fsck/k9/mail/store/Pop3Store.java b/src/com/fsck/k9/mail/store/Pop3Store.java
index ab2133001..bdc0ef5bf 100644
--- a/src/com/fsck/k9/mail/store/Pop3Store.java
+++ b/src/com/fsck/k9/mail/store/Pop3Store.java
@@ -27,6 +27,7 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 public class Pop3Store extends Store {
     public static final String STORE_TYPE = "POP3";
@@ -628,7 +629,7 @@ public class Pop3Store extends Store {
 
         private void indexUids(ArrayList<String> uids)
         throws MessagingException, IOException {
-            HashSet<String> unindexedUids = new HashSet<String>();
+            Set<String> unindexedUids = new HashSet<String>();
             for (String uid : uids) {
                 if (mUidToMsgMap.get(uid) == null) {
                     if (K9.DEBUG && K9.DEBUG_PROTOCOL_POP3) {
@@ -801,7 +802,7 @@ public class Pop3Store extends Store {
                     }
                 }
             } else {
-                HashSet<String> msgUidIndex = new HashSet<String>();
+                Set<String> msgUidIndex = new HashSet<String>();
                 for (Message message : messages) {
                     msgUidIndex.add(message.getUid());
                 }
diff --git a/src/com/fsck/k9/search/ConditionsTreeNode.java b/src/com/fsck/k9/search/ConditionsTreeNode.java
index 1a1be85d7..7730e0725 100644
--- a/src/com/fsck/k9/search/ConditionsTreeNode.java
+++ b/src/com/fsck/k9/search/ConditionsTreeNode.java
@@ -4,6 +4,7 @@ import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Stack;
+import java.util.Set;
 
 import android.database.Cursor;
 import android.os.Parcel;
@@ -243,8 +244,8 @@ public class ConditionsTreeNode implements Parcelable {
      * Get a set of all the leaves in the tree.
      * @return Set of all the leaves.
      */
-    public HashSet<ConditionsTreeNode> getLeafSet() {
-        HashSet<ConditionsTreeNode> leafSet = new HashSet<ConditionsTreeNode>();
+    public Set<ConditionsTreeNode> getLeafSet() {
+        Set<ConditionsTreeNode> leafSet = new HashSet<ConditionsTreeNode>();
         return getLeafSet(leafSet);
     }
 
@@ -338,7 +339,7 @@ public class ConditionsTreeNode implements Parcelable {
      * @param leafSet Leafset that's being built.
      * @return Set of leaves being completed.
      */
-    private HashSet<ConditionsTreeNode> getLeafSet(HashSet<ConditionsTreeNode> leafSet) {
+    private Set<ConditionsTreeNode> getLeafSet(Set<ConditionsTreeNode> leafSet) {
         if (mLeft == null && mRight == null) {
             // if we ended up in a leaf, add ourself and return
             leafSet.add(this);
diff --git a/src/com/fsck/k9/search/LocalSearch.java b/src/com/fsck/k9/search/LocalSearch.java
index 9ee9577e9..e109e50f4 100644
--- a/src/com/fsck/k9/search/LocalSearch.java
+++ b/src/com/fsck/k9/search/LocalSearch.java
@@ -28,9 +28,9 @@ public class LocalSearch implements SearchSpecification {
     private boolean mManualSearch = false;
 
     // since the uuid isn't in the message table it's not in the tree neither
-    private HashSet<String> mAccountUuids = new HashSet<String>();
+    private Set<String> mAccountUuids = new HashSet<String>();
     private ConditionsTreeNode mConditions = null;
-    private HashSet<ConditionsTreeNode> mLeafSet = new HashSet<ConditionsTreeNode>();
+    private Set<ConditionsTreeNode> mLeafSet = new HashSet<ConditionsTreeNode>();
 
 
     ///////////////////////////////////////////////////////////////