diff --git a/proto/protocol.xml b/proto/protocol.xml
index 9deb324..c6144b6 100644
--- a/proto/protocol.xml
+++ b/proto/protocol.xml
@@ -396,7 +396,7 @@
         the ei_callback object is destroyed by the EIS implementation and as such the
         client must not attempt to use it after that point.
       </description>
-      <arg name="callback_data" type="uint32" summary="request-specific data for the callback"/>
+      <arg name="callback_data" type="uint64" summary="request-specific data for the callback"/>
     </event>
   </interface>
 
@@ -418,7 +418,7 @@
         the ei_pingpong object is destroyed by the client and as such must not be used
         any further.
       </description>
-      <arg name="callback_data" type="uint32" summary="request-specific data for the callback"/>
+      <arg name="callback_data" type="uint64" summary="request-specific data for the callback"/>
     </request>
 
     <!-- ei_pingpong events version 1 -->
diff --git a/src/libei-callback.c b/src/libei-callback.c
index 6acec2f..df699f2 100644
--- a/src/libei-callback.c
+++ b/src/libei-callback.c
@@ -69,7 +69,7 @@ ei_callback_get_id(struct ei_callback *callback)
 }
 
 static struct brei_result *
-handle_msg_done(struct ei_callback *callback, uint32_t callback_data)
+handle_msg_done(struct ei_callback *callback, uint64_t callback_data)
 {
 	callback->func(callback, callback->callback_data, callback_data);
 	return NULL;
diff --git a/src/libei-callback.h b/src/libei-callback.h
index e2744f4..585e6c3 100644
--- a/src/libei-callback.h
+++ b/src/libei-callback.h
@@ -32,7 +32,9 @@
 struct ei;
 struct ei_callback;
 
-typedef void (*ei_callback_func)(struct ei_callback *callback, void *callback_data, uint32_t proto_data);
+typedef void (*ei_callback_func)(struct ei_callback *callback,
+				 void *callback_data,
+				 uint64_t proto_data);
 
 /* This is a protocol-only object, not exposed in the API */
 struct ei_callback {
diff --git a/src/libei-connection.c b/src/libei-connection.c
index f342089..61c8d7a 100644
--- a/src/libei-connection.c
+++ b/src/libei-connection.c
@@ -107,7 +107,7 @@ struct callback_user_data {
 };
 
 static void
-sync_callback(struct ei_callback *callback, void *callback_data, uint32_t proto_data)
+sync_callback(struct ei_callback *callback, void *callback_data, uint64_t proto_data)
 {
 	struct ei_connection *connection = callback_data;
 
diff --git a/src/libeis-connection.c b/src/libeis-connection.c
index 167701c..f470578 100644
--- a/src/libeis-connection.c
+++ b/src/libeis-connection.c
@@ -114,7 +114,8 @@ struct pingpong_user_data {
 };
 
 static void
-ping_pingpong(struct eis_pingpong *pingpong, void *pingpong_data, uint32_t proto_data)
+ping_pingpong(struct eis_pingpong *pingpong, void *pingpong_data,
+	      uint64_t proto_data)
 {
 	struct eis_connection *connection = pingpong_data;
 
diff --git a/src/libeis-pingpong.c b/src/libeis-pingpong.c
index 3c02fb9..b35101d 100644
--- a/src/libeis-pingpong.c
+++ b/src/libeis-pingpong.c
@@ -81,7 +81,7 @@ eis_pingpong_get_version(struct eis_pingpong *pingpong)
 }
 
 static struct brei_result *
-client_msg_done(struct eis_pingpong *pingpong, uint32_t pingpong_data)
+client_msg_done(struct eis_pingpong *pingpong, uint64_t pingpong_data)
 {
 	pingpong->func(pingpong, pingpong->pingpong_data, pingpong_data);
 	return NULL;
diff --git a/src/libeis-pingpong.h b/src/libeis-pingpong.h
index 551296a..7ea26d7 100644
--- a/src/libeis-pingpong.h
+++ b/src/libeis-pingpong.h
@@ -32,7 +32,9 @@ struct eis;
 struct eis_client;
 struct eis_pingpong;
 
-typedef void (*eis_pingpong_func)(struct eis_pingpong *pingpong, void *pingpong_data, uint32_t proto_data);
+typedef void (*eis_pingpong_func)(struct eis_pingpong *pingpong,
+				  void *pingpong_data,
+				  uint64_t proto_data);
 
 /* This is a protocol-only object, not exposed in the API */
 struct eis_pingpong {