diff --git a/src/interned_string.cc b/src/interned_string.cc
index fb6898c0..0755e3d4 100644
--- a/src/interned_string.cc
+++ b/src/interned_string.cc
@@ -28,7 +28,7 @@ InternedString StringRegistry::acquire(StringView str)
     auto it = m_slot_map.find(str);
     if (it == m_slot_map.end())
     {
-        size_t slot;
+        Slot slot;
         if (not m_free_slots.empty())
         {
             slot = m_free_slots.back();
@@ -48,20 +48,20 @@ InternedString StringRegistry::acquire(StringView str)
         return InternedString{storage_view, slot};
     }
 
-    size_t slot = it->second;
+    Slot slot = it->second;
     auto& data = m_storage[slot];
     ++data.refcount;
     return {{data.data.data(), (int)data.data.size()}, slot};
 }
 
-void StringRegistry::acquire(size_t slot)
+void StringRegistry::acquire(Slot slot)
 {
     kak_assert(slot < m_storage.size());
     kak_assert(m_storage[slot].refcount > 0);
     ++m_storage[slot].refcount;
 }
 
-void StringRegistry::release(size_t slot) noexcept
+void StringRegistry::release(Slot slot) noexcept
 {
     kak_assert(m_storage[slot].refcount > 0);
     if (--m_storage[slot].refcount == 0)
diff --git a/src/interned_string.hh b/src/interned_string.hh
index 66c7bd58..b74653b7 100644
--- a/src/interned_string.hh
+++ b/src/interned_string.hh
@@ -6,6 +6,8 @@
 #include "unordered_map.hh"
 #include "vector.hh"
 
+#include <cstddef>
+
 namespace Kakoune
 {
 
@@ -17,13 +19,14 @@ public:
     void debug_stats() const;
 private:
     friend class InternedString;
+    using Slot = uint32_t;
 
     InternedString acquire(StringView str);
-    void acquire(size_t slot);
-    void release(size_t slot) noexcept;
+    void acquire(Slot slot);
+    void release(Slot slot) noexcept;
 
-    UnorderedMap<StringView, size_t, MemoryDomain::InternedString> m_slot_map;
-    Vector<size_t, MemoryDomain::InternedString> m_free_slots;
+    UnorderedMap<StringView, Slot, MemoryDomain::InternedString> m_slot_map;
+    Vector<Slot, MemoryDomain::InternedString> m_free_slots;
     struct DataAndRefCount
     {
         Vector<char, MemoryDomain::InternedString> data;
@@ -101,7 +104,7 @@ public:
 private:
     friend class StringRegistry;
 
-    InternedString(StringView str, size_t slot)
+    InternedString(StringView str, StringRegistry::Slot slot)
         : StringView(str), m_slot(slot) {}
 
     void acquire_ifn(StringView str)
@@ -121,7 +124,7 @@ private:
             StringRegistry::instance().release(m_slot);
     }
 
-    size_t m_slot = -1;
+    StringRegistry::Slot m_slot = -1;
 };
 
 inline size_t hash_value(const Kakoune::InternedString& str)