Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -22,10 +22,12 @@
 CPPFLAGS="$CPPFLAGS $OBJCPPFLAGS $($OBJFW_CONFIG --cppflags)"
 OBJCFLAGS="$OBJCFLAGS -Wall $($OBJFW_CONFIG --objcflags)"
 LDFLAGS="$LDFLAGS $($OBJFW_CONFIG --ldflags)"
 LIBS="$LIBS $($OBJFW_CONFIG --libs)"
 
+AX_CHECK_COMPILER_FLAGS(-Watomic-properties,
+	[OBJCFLAGS="$OBJCFLAGS -Watomic-properties"])
 AX_CHECK_COMPILER_FLAGS(-Wdocumentation,
 	[OBJCFLAGS="$OBJCFLAGS -Wdocumentation"])
 
 AC_ARG_ENABLE(shared,
 	AS_HELP_STRING([--disable-shared], [do not build shared library]))

Index: src/XMPPConnection.h
==================================================================
--- src/XMPPConnection.h
+++ src/XMPPConnection.h
@@ -217,41 +217,41 @@
 @property (readonly, nonatomic) XMPPJID *JID;
 
 /*!
  * The port to connect to.
  */
-@property uint16_t port;
+@property (nonatomic) uint16_t port;
 
 /*!
  * An object for data storage, conforming to the XMPPStorage protocol.
  */
-@property OF_NULLABLE_PROPERTY (assign) id <XMPPStorage> dataStorage;
+@property OF_NULLABLE_PROPERTY (nonatomic, assign) id <XMPPStorage> dataStorage;
 
 /*!
  * The socket used for the connection.
  */
 @property (readonly, nonatomic) OFTCPSocket *socket;
 
 /*!
  * Whether encryption is required.
  */
-@property bool encryptionRequired;
+@property (nonatomic) bool encryptionRequired;
 
 /*!
  * Whether the connection is encrypted.
  */
-@property (readonly) bool encrypted;
+@property (readonly, nonatomic) bool encrypted;
 
 /*!
  * Whether roster versioning is supported.
  */
-@property (readonly) bool supportsRosterVersioning;
+@property (readonly, nonatomic) bool supportsRosterVersioning;
 
 /*!
  * Whether stream management is supported.
  */
-@property (readonly) bool supportsStreamManagement;
+@property (readonly, nonatomic) bool supportsStreamManagement;
 
 /*!
  * Creates a new autoreleased XMPPConnection.
  *
  * @return A new autoreleased XMPPConnection

Index: src/XMPPDiscoEntity.h
==================================================================
--- src/XMPPDiscoEntity.h
+++ src/XMPPDiscoEntity.h
@@ -46,16 +46,16 @@
  *	  responses for
  *
  * This usually contains at least all immediate child nodes, but may contain
  * any number of nodes nested more deeply.
  */
-@property (readonly) OFDictionary *discoNodes;
+@property (readonly, nonatomic) OFDictionary *discoNodes;
 
 /*!
  * The node advertised for the entity's capabilites.
  */
-@property (readonly) OFString *capsNode;
+@property (readonly, nonatomic) OFString *capsNode;
 
 + (instancetype)discoNodeWithJID: (XMPPJID *)JID
 			    node: (nullable OFString *)node OF_UNAVAILABLE;
 + (instancetype)discoNodeWithJID: (XMPPJID *)JID
 			    node: (nullable OFString *)node

Index: src/XMPPMessage.h
==================================================================
--- src/XMPPMessage.h
+++ src/XMPPMessage.h
@@ -27,12 +27,14 @@
 
 /*!
  * @brief A class describing a message stanza.
  */
 @interface XMPPMessage: XMPPStanza
-/*! The text content of the body of the message. */
-@property (copy) OFString *body;
+/*!
+ * The text content of the body of the message.
+ */
+@property (nonatomic, copy) OFString *body;
 
 /*!
  * @brief Creates a new autoreleased XMPPMessage.
  *
  * @return A new autoreleased XMPPMessage

Index: src/XMPPRoster.h
==================================================================
--- src/XMPPRoster.h
+++ src/XMPPRoster.h
@@ -70,11 +70,11 @@
 }
 
 /*!
  * @brief The connection to which the roster belongs
  */
-@property (readonly, assign) XMPPConnection *connection;
+@property (readonly, nonatomic) XMPPConnection *connection;
 
 /*!
  * @brief An object for data storage, conforming to the XMPPStorage protocol.
  *
  * Inherited from the connection if not overridden.

Index: src/XMPPSRVLookup.h
==================================================================
--- src/XMPPSRVLookup.h
+++ src/XMPPSRVLookup.h
@@ -36,14 +36,14 @@
 	uint32_t _accumulatedWeight;
 	uint16_t _port;
 	OFString *_target;
 }
 
-@property (readonly) uint16_t priority;
-@property (readonly) uint16_t weight;
-@property uint32_t accumulatedWeight;
-@property (readonly) uint16_t port;
+@property (readonly, nonatomic) uint16_t priority;
+@property (readonly, nonatomic) uint16_t weight;
+@property (nonatomic) uint32_t accumulatedWeight;
+@property (readonly, nonatomic) uint16_t port;
 @property (readonly, nonatomic) OFString *target;
 
 + (instancetype)entryWithPriority: (uint16_t)priority
 			   weight: (uint16_t)weight
 			     port: (uint16_t)port