diff --git a/.idea/codeStyleSettings.xml b/.idea/codeStyleSettings.xml
index 2feaa4e95..a7a72e1fb 100644
--- a/.idea/codeStyleSettings.xml
+++ b/.idea/codeStyleSettings.xml
@@ -31,6 +31,8 @@
           </value>
         </option>
         <option name="RIGHT_MARGIN" value="100" />
+        <option name="JD_ALIGN_PARAM_COMMENTS" value="false" />
+        <option name="JD_ALIGN_EXCEPTION_COMMENTS" value="false" />
         <AndroidXmlCodeStyleSettings>
           <option name="USE_CUSTOM_SETTINGS" value="true" />
         </AndroidXmlCodeStyleSettings>
diff --git a/briar-api/src/org/briarproject/api/privategroup/invitation/GroupInvitationManager.java b/briar-api/src/org/briarproject/api/privategroup/invitation/GroupInvitationManager.java
index 2a4d4539f..59475c974 100644
--- a/briar-api/src/org/briarproject/api/privategroup/invitation/GroupInvitationManager.java
+++ b/briar-api/src/org/briarproject/api/privategroup/invitation/GroupInvitationManager.java
@@ -1,5 +1,6 @@
 package org.briarproject.api.privategroup.invitation;
 
+import org.briarproject.api.clients.ProtocolStateException;
 import org.briarproject.api.clients.SessionId;
 import org.briarproject.api.contact.Contact;
 import org.briarproject.api.contact.ContactId;
@@ -26,18 +27,28 @@ public interface GroupInvitationManager {
 	/**
 	 * Sends an invitation to share the given private group with the given
 	 * contact, including an optional message.
+	 *
+	 * @throws ProtocolStateException if the group is no longer eligible to be
+	 * shared with the contact, for example because an invitation is already
+	 * pending.
 	 */
 	void sendInvitation(GroupId g, ContactId c, @Nullable String message,
 			long timestamp, byte[] signature) throws DbException;
 
 	/**
 	 * Responds to a pending private group invitation from the given contact.
+	 *
+	 * @throws ProtocolStateException if the invitation is no longer pending,
+	 * for example because the group has been dissolved.
 	 */
 	void respondToInvitation(ContactId c, PrivateGroup g, boolean accept)
 			throws DbException;
 
 	/**
 	 * Responds to a pending private group invitation from the given contact.
+	 *
+	 * @throws ProtocolStateException if the invitation is no longer pending,
+	 * for example because the group has been dissolved.
 	 */
 	void respondToInvitation(ContactId c, SessionId s, boolean accept)
 			throws DbException;
@@ -45,6 +56,9 @@ public interface GroupInvitationManager {
 	/**
 	 * Makes the user's relationship with the given contact visible to the
 	 * given private group.
+	 *
+	 * @throws ProtocolStateException if the relationship is no longer eligible
+	 * to be revealed, for example because the contact has revealed it.
 	 */
 	void revealRelationship(ContactId c, GroupId g) throws DbException;
 
diff --git a/briar-core/src/org/briarproject/privategroup/invitation/GroupInvitationManagerImpl.java b/briar-core/src/org/briarproject/privategroup/invitation/GroupInvitationManagerImpl.java
index bc6dd88f6..d4a51798f 100644
--- a/briar-core/src/org/briarproject/privategroup/invitation/GroupInvitationManagerImpl.java
+++ b/briar-core/src/org/briarproject/privategroup/invitation/GroupInvitationManagerImpl.java
@@ -459,9 +459,6 @@ class GroupInvitationManagerImpl extends ConversationClientImpl
 			db.commitTransaction(txn);
 			// If there's no session, the contact can be invited
 			if (ss == null) return true;
-			// If there's a session, it should be a creator session
-			if (sessionParser.getRole(ss.bdfSession) != CREATOR)
-				throw new IllegalArgumentException();
 			// If the session's in the start state, the contact can be invited
 			CreatorSession session = sessionParser
 					.parseCreatorSession(contactGroupId, ss.bdfSession);