diff --git a/hashtable.hxx.in b/hashtable.hxx.in
index 1ce19d67c5bf10c657a04cea0c8237d4b3ef9ec9..a60f5d91435a34fe0b31c31120dcc21729b885b5 100644
--- a/hashtable.hxx.in
+++ b/hashtable.hxx.in
@@ -232,7 +232,7 @@ public:
   typedef T value_type;
 
   hash_allocator() throw(): alloc_() {}
-  hash_allocator(const hash_allocator_base& a) throw() : alloc_() {}
+  hash_allocator(const hash_allocator_base&) throw() : alloc_() {}
   hash_allocator(const hash_allocator& a) throw() : alloc_(a.alloc_) {}
   hash_allocator(const alloc_type& a) throw() : alloc_(a) {}
   ~hash_allocator() throw() {}