diff --git a/libuavcan/include/uavcan/internal/transport/transfer.hpp b/libuavcan/include/uavcan/internal/transport/transfer.hpp
index efc5d94188..faf5904326 100644
--- a/libuavcan/include/uavcan/internal/transport/transfer.hpp
+++ b/libuavcan/include/uavcan/internal/transport/transfer.hpp
@@ -27,6 +27,12 @@ enum TransferType
     NUM_TRANSFER_TYPES = 4
 };
 
+enum DataTypeKind
+{
+    DATA_TYPE_KIND_SERVICE,
+    DATA_TYPE_KIND_MESSAGE,
+    NUM_DATA_TYPE_KINDS
+};
 
 class TransferID
 {
diff --git a/libuavcan/include/uavcan/internal/transport/transfer_id_registry.hpp b/libuavcan/include/uavcan/internal/transport/transfer_id_registry.hpp
index c897fbc88f..ccf59b9651 100644
--- a/libuavcan/include/uavcan/internal/transport/transfer_id_registry.hpp
+++ b/libuavcan/include/uavcan/internal/transport/transfer_id_registry.hpp
@@ -19,18 +19,18 @@ class TransferIDRegistry
 public:
     struct Key
     {
-        TransferType transfer_type;
+        DataTypeKind data_type_kind;
         uint16_t data_type_id;
         uint8_t node_id;
 
         Key()
-        : transfer_type(TransferType(0))
+        : data_type_kind(DataTypeKind(0))
         , data_type_id(0)
         , node_id(NODE_ID_INVALID)
         { }
 
-        Key(uint8_t node_id, TransferType transfer_type, uint16_t data_type_id)
-        : transfer_type(transfer_type)
+        Key(uint8_t node_id, DataTypeKind data_type_kind, uint16_t data_type_id)
+        : data_type_kind(data_type_kind)
         , data_type_id(data_type_id)
         , node_id(node_id)
         { }
@@ -105,7 +105,7 @@ private:
         void compact(IAllocator* allocator);
     };
 
-    List lists_by_transfer_type_[NUM_TRANSFER_TYPES];
+    List lists_by_data_type_kind_[NUM_DATA_TYPE_KINDS];
     IAllocator* const allocator_;
 
 public:
@@ -128,9 +128,9 @@ public:
     template <typename Predicate>
     void removeWhere(Predicate predicate)
     {
-        for (int transfer_type = 0; transfer_type < NUM_TRANSFER_TYPES; transfer_type++)
+        for (int data_type_kind = 0; data_type_kind < NUM_DATA_TYPE_KINDS; data_type_kind++)
         {
-            StorageEntryGroup* p = lists_by_transfer_type_[transfer_type].getHead();
+            StorageEntryGroup* p = lists_by_data_type_kind_[data_type_kind].getHead();
             while (p)
             {
                 for (int i = 0; i < StorageEntryGroup::NUM_ENTRIES; i++)
@@ -138,7 +138,7 @@ public:
                     const StorageEntry* const entry = p->entries + i;
                     if (!entry->isEmpty())
                     {
-                        const Key key(entry->node_id, TransferType(transfer_type), entry->data_type_id);
+                        const Key key(entry->node_id, DataTypeKind(data_type_kind), entry->data_type_id);
                         const bool result = predicate(key, static_cast<const Entry&>(*entry));
                         if (result)
                             p->entries[i] = StorageEntry();
@@ -146,7 +146,7 @@ public:
                 }
                 p = p->getNextListNode();
             }
-            lists_by_transfer_type_[transfer_type].compact(allocator_);
+            lists_by_data_type_kind_[data_type_kind].compact(allocator_);
         }
     }
 };
diff --git a/libuavcan/src/transport/transfer_id_registry.cpp b/libuavcan/src/transport/transfer_id_registry.cpp
index 7561615205..d5f413fb91 100644
--- a/libuavcan/src/transport/transfer_id_registry.cpp
+++ b/libuavcan/src/transport/transfer_id_registry.cpp
@@ -101,33 +101,33 @@ void TransferIDRegistry::List::compact(IAllocator* allocator)
  */
 TransferIDRegistry::Entry* TransferIDRegistry::access(const Key& key)
 {
-    if (key.node_id > NODE_ID_MAX || key.transfer_type >= NUM_TRANSFER_TYPES)
+    if (key.node_id > NODE_ID_MAX || key.data_type_kind >= NUM_DATA_TYPE_KINDS)
     {
         assert(0);
         return NULL;
     }
-    return static_cast<Entry*>(lists_by_transfer_type_[key.transfer_type].find(key));
+    return static_cast<Entry*>(lists_by_data_type_kind_[key.data_type_kind].find(key));
 }
 
 bool TransferIDRegistry::create(const Key& key, const Entry& entry)
 {
-    if (key.node_id > NODE_ID_MAX || key.transfer_type >= NUM_TRANSFER_TYPES)
+    if (key.node_id > NODE_ID_MAX || key.data_type_kind >= NUM_DATA_TYPE_KINDS)
     {
         assert(0);
         return false;
     }
-    return lists_by_transfer_type_[key.transfer_type].create(
+    return lists_by_data_type_kind_[key.data_type_kind].create(
         StorageEntry(key.node_id, key.data_type_id, entry), allocator_);
 }
 
 void TransferIDRegistry::remove(const Key& key)
 {
-    if (key.node_id > NODE_ID_MAX || key.transfer_type >= NUM_TRANSFER_TYPES)
+    if (key.node_id > NODE_ID_MAX || key.data_type_kind >= NUM_DATA_TYPE_KINDS)
     {
         assert(0);
         return;
     }
-    lists_by_transfer_type_[key.transfer_type].remove(key, allocator_);
+    lists_by_data_type_kind_[key.data_type_kind].remove(key, allocator_);
 }
 
 }
diff --git a/libuavcan/test/transport/transfer_id_registry.cpp b/libuavcan/test/transport/transfer_id_registry.cpp
index 75ce7d0a05..d8db4fcce9 100644
--- a/libuavcan/test/transport/transfer_id_registry.cpp
+++ b/libuavcan/test/transport/transfer_id_registry.cpp
@@ -20,7 +20,7 @@ TEST(TransferIDRegistry, Basic)
 {
     using uavcan::Frame;
     using uavcan::TransferID;
-    using uavcan::TransferType;
+    using uavcan::DataTypeKind;
     using uavcan::TransferIDRegistry;
     typedef TransferIDRegistry::Key Key;
     typedef TransferIDRegistry::Entry Entry;
@@ -32,7 +32,7 @@ TEST(TransferIDRegistry, Basic)
 
     TransferIDRegistry reg(&poolmgr);
 
-    ASSERT_EQ(NULL, reg.access(Key(0, uavcan::MESSAGE_BROADCAST, 0)));
+    ASSERT_EQ(NULL, reg.access(Key(0, uavcan::DATA_TYPE_KIND_MESSAGE, 0)));
 
     static const int NUM_ITEMS = 100;    // Just to make sure it will be enough
     Key keys[NUM_ITEMS];
@@ -44,7 +44,7 @@ TEST(TransferIDRegistry, Basic)
     {
         keys[i].data_type_id = i * (Frame::DATA_TYPE_ID_MAX / NUM_ITEMS);
         keys[i].node_id = i * (uavcan::NODE_ID_MAX / NUM_ITEMS);
-        keys[i].transfer_type = TransferType(i % uavcan::NUM_TRANSFER_TYPES);
+        keys[i].data_type_kind = DataTypeKind(i % uavcan::NUM_DATA_TYPE_KINDS);
 
         entries[i].timestamp = i * 10000000;
         entries[i].transfer_id = TransferID(i % TransferID::MAX);