diff --git a/base-hw/src/core/include/cpu_thread_allocator.h b/base-hw/src/core/include/cpu_thread_allocator.h
index bd699b4c4b..f930816c7c 100644
--- a/base-hw/src/core/include/cpu_thread_allocator.h
+++ b/base-hw/src/core/include/cpu_thread_allocator.h
@@ -50,18 +50,19 @@ namespace Genode
 				_alloc->free(addr, size); }
 
 			size_t consumed() {
-				PDBG("Unexprected call");
+				PDBG("Unexpected call");
 				while (1) ;
 				return 0;
 			}
 
 			size_t overhead(size_t size) {
-				PDBG("Unexprected call");
+				PDBG("Unexpected call");
 				while (1) ;
 				return 0;
 			}
 
-			bool need_size_for_free() const { return true; }
+			bool need_size_for_free() const override {
+				return _alloc->need_size_for_free(); }
 	};
 }
 
diff --git a/base-linux/src/core/include/platform.h b/base-linux/src/core/include/platform.h
index 477e3c17ba..34fa3d804d 100644
--- a/base-linux/src/core/include/platform.h
+++ b/base-linux/src/core/include/platform.h
@@ -65,6 +65,8 @@ namespace Genode {
 				size_t avail()                      { return ~0; }
 				bool   valid_addr(addr_t)           { return true; }
 				size_t overhead(size_t)             { return 0; }
+
+				bool need_size_for_free() const override { return true; }
 			};
 
 			Pseudo_ram_allocator _ram_alloc;
diff --git a/base/include/base/allocator.h b/base/include/base/allocator.h
index c59aeee379..55a6da8c99 100644
--- a/base/include/base/allocator.h
+++ b/base/include/base/allocator.h
@@ -39,7 +39,7 @@ namespace Genode {
 		 * See the documentation of 'operator delete(void *, Allocator *)'
 		 * below for more details.
 		 */
-		virtual bool need_size_for_free() const { return true; }
+		virtual bool need_size_for_free() const = 0;
 	};
 
 
diff --git a/base/include/base/allocator_avl.h b/base/include/base/allocator_avl.h
index dd0394121b..b7eba7d33f 100644
--- a/base/include/base/allocator_avl.h
+++ b/base/include/base/allocator_avl.h
@@ -243,7 +243,7 @@ namespace Genode {
 			 */
 			size_t overhead(size_t) { return sizeof(Block) + sizeof(umword_t); }
 
-			bool need_size_for_free() const { return false; }
+			bool need_size_for_free() const override { return false; }
 	};
 
 
diff --git a/base/include/base/allocator_guard.h b/base/include/base/allocator_guard.h
index 9fd25c68ee..1feba9859a 100644
--- a/base/include/base/allocator_guard.h
+++ b/base/include/base/allocator_guard.h
@@ -103,6 +103,9 @@ namespace Genode {
 			 * Return meta-data overhead per block
 			 */
 			size_t overhead(size_t size) { return _allocator->overhead(size); }
+
+			bool need_size_for_free() const override {
+				return _allocator->need_size_for_free(); }
 	};
 }
 
diff --git a/base/include/base/heap.h b/base/include/base/heap.h
index ba0368e528..ba4494ae2c 100644
--- a/base/include/base/heap.h
+++ b/base/include/base/heap.h
@@ -153,7 +153,7 @@ namespace Genode {
 			void   free(void *, size_t);
 			size_t consumed() { return _quota_used; }
 			size_t overhead(size_t size) { return _alloc.overhead(size); }
-			bool   need_size_for_free() const { return false; }
+			bool   need_size_for_free() const override { return false; }
 	};
 
 
@@ -193,7 +193,7 @@ namespace Genode {
 			void   free(void *, size_t);
 			size_t consumed() { return _consumed; }
 			size_t overhead(size_t size);
-			bool   need_size_for_free() const { return false; }
+			bool   need_size_for_free() const override { return false; }
 	};
 }
 
diff --git a/base/include/base/slab.h b/base/include/base/slab.h
index aa246de7b6..25aad44156 100644
--- a/base/include/base/slab.h
+++ b/base/include/base/slab.h
@@ -249,7 +249,7 @@ namespace Genode {
 			void   free(void *addr, size_t) { free(addr); }
 			size_t consumed();
 			size_t overhead(size_t) { return _block_size/_num_elem; }
-			bool   need_size_for_free() const { return false; }
+			bool   need_size_for_free() const override { return false; }
 	};
 }
 
diff --git a/base/include/base/sync_allocator.h b/base/include/base/sync_allocator.h
index 3f0273564b..8042fe2182 100644
--- a/base/include/base/sync_allocator.h
+++ b/base/include/base/sync_allocator.h
@@ -92,6 +92,12 @@ namespace Genode {
 				Lock::Guard lock_guard(*_lock);
 				return _alloc.overhead(size);
 			}
+
+			bool need_size_for_free() const override
+			{
+				Lock::Guard lock_guard(*_lock);
+				return _alloc.need_size_for_free();
+			}
 	};
 
 	/**
@@ -191,6 +197,12 @@ namespace Genode {
 				return _alloc.overhead(size);
 			}
 
+			bool need_size_for_free() const override
+			{
+				Lock::Guard lock_guard(*_lock);
+				return _alloc.need_size_for_free();
+			}
+
 
 			/*******************************
 			 ** Range-allocator interface **
diff --git a/base/src/core/include/core_mem_alloc.h b/base/src/core/include/core_mem_alloc.h
index 83115aa4c4..1717a0e8fd 100644
--- a/base/src/core/include/core_mem_alloc.h
+++ b/base/src/core/include/core_mem_alloc.h
@@ -88,6 +88,9 @@ namespace Genode {
 					void free(void *addr, size_t size) { _alloc.free(addr, size); }
 					size_t consumed() { return _phys_alloc->consumed(); }
 					size_t overhead(size_t size) { return _phys_alloc->overhead(size); }
+
+					bool need_size_for_free() const override {
+						return _phys_alloc->need_size_for_free(); }
 			};
 
 
@@ -166,6 +169,9 @@ namespace Genode {
 
 			size_t consumed() { return _phys_alloc.consumed(); }
 			size_t overhead(size_t size) { return _phys_alloc.overhead(size); }
+
+			bool need_size_for_free() const override {
+				return _phys_alloc.need_size_for_free(); }
 	};
 }
 
diff --git a/dde_linux/src/lib/lxip/lxcc_emul.cc b/dde_linux/src/lib/lxip/lxcc_emul.cc
index 60917e4258..a851304b44 100644
--- a/dde_linux/src/lib/lxip/lxcc_emul.cc
+++ b/dde_linux/src/lib/lxip/lxcc_emul.cc
@@ -115,6 +115,7 @@ class Genode::Slab_backend_alloc : public Genode::Allocator,
 
 		void   free(void *addr, size_t /* size */) { }
 		size_t overhead(size_t size) { return  0; }
+		bool need_size_for_free() const override { return false; }
 
 		/**
 		 * Return phys address for given virtual addr.
diff --git a/dde_linux/src/lib/usb/lx_emul.cc b/dde_linux/src/lib/usb/lx_emul.cc
index d71c3424a2..f1f1659da6 100644
--- a/dde_linux/src/lib/usb/lx_emul.cc
+++ b/dde_linux/src/lib/usb/lx_emul.cc
@@ -117,6 +117,7 @@ class Genode::Slab_backend_alloc : public Genode::Allocator,
 
 		void   free(void *addr, size_t /* size */) { }
 		size_t overhead(size_t size) { return  0; }
+		bool need_size_for_free() const override { return false; }
 
 		/**
 		 * Return phys address for given virtual addr.
diff --git a/libports/src/lib/libc/malloc.cc b/libports/src/lib/libc/malloc.cc
index ecf1fd6247..8173365e96 100644
--- a/libports/src/lib/libc/malloc.cc
+++ b/libports/src/lib/libc/malloc.cc
@@ -150,6 +150,8 @@ class Malloc : public Genode::Allocator
 
 			return _allocator[_slab_log2(size) - SLAB_START]->overhead(size);
 		}
+
+		bool need_size_for_free() const override { return false; }
 };
 
 
diff --git a/os/include/nic/packet_allocator.h b/os/include/nic/packet_allocator.h
index 8fe335f159..4f2c13166b 100644
--- a/os/include/nic/packet_allocator.h
+++ b/os/include/nic/packet_allocator.h
@@ -112,6 +112,8 @@ namespace Nic {
 
 			void free(void *addr, Genode::size_t) { free(addr); }
 
+			bool need_size_for_free() const override { return false; }
+
 
 			/*********************
 			 ** Dummy functions **
diff --git a/os/src/lib/dde_kit/memory.cc b/os/src/lib/dde_kit/memory.cc
index cf3ced267c..2dc41326c4 100644
--- a/os/src/lib/dde_kit/memory.cc
+++ b/os/src/lib/dde_kit/memory.cc
@@ -155,6 +155,8 @@ class Backing_store_allocator : public Allocator
 		size_t consumed() { return _consumed; }
 
 		size_t overhead(size_t size) { return 0; }
+
+		bool need_size_for_free() const override { return false; }
 };
 
 
diff --git a/os/src/test/ram_fs_chunk/main.cc b/os/src/test/ram_fs_chunk/main.cc
index 3d9ad3de12..5d4dc1c4a4 100644
--- a/os/src/test/ram_fs_chunk/main.cc
+++ b/os/src/test/ram_fs_chunk/main.cc
@@ -42,7 +42,8 @@ namespace Genode {
 			_wrapped.free(addr, size);
 		}
 
-		size_t overhead(size_t size) { return 0; }
+		size_t overhead(size_t size)    override { return _wrapped.overhead(size); }
+		bool need_size_for_free() const override { return _wrapped.need_size_for_free(); }
 	};
 };