diff --git a/repos/ports/src/virtualbox5/spec/nova/sup.cc b/repos/ports/src/virtualbox5/spec/nova/sup.cc
index af2d20b3f..3bd9fcf9d 100644
--- a/repos/ports/src/virtualbox5/spec/nova/sup.cc
+++ b/repos/ports/src/virtualbox5/spec/nova/sup.cc
@@ -64,14 +64,22 @@ enum {
 };
 
 typedef Genode::Bit_allocator<HANDY_PAGES>   Page_ids;
-typedef Genode::Bit_allocator<MAX_CHUNK_IDS> Chunk_ids;
-typedef Genode::Bit_array<PAGES_SUPERPAGE>    Free_ids;
+typedef Genode::Bit_array<PAGES_SUPERPAGE>   Free_ids;
+
+class Chunk_ids: public Genode::Bit_allocator<MAX_CHUNK_IDS>
+{
+	public:
+
+		void reserve(Genode::addr_t bit_start, size_t const num) {
+			_reserve(bit_start, num); };
+};
 
 static Page_ids  page_ids;
 static Chunk_ids chunk_ids;
 
 
-static Sub_rm_connection &vm_memory(Genode::addr_t vm_size = 0)
+
+static Sub_rm_connection &vm_memory(Genode::uint64_t vm_size = 0)
 {
 	/* memory used by the VM in any order as the VMM asks for allocations */
 	static Sub_rm_connection vm_memory(genode_env(), vm_size);
@@ -113,6 +121,12 @@ static Sub_rm_connection &vm_memory(Genode::addr_t vm_size = 0)
 		memory = fli.page();
 	}
 
+	/* reserve chunkids which are special or unused */
+	chunk_ids.reserve(0, CHUNKID_START);
+	addr_t const unused_id = CHUNKID_START + vm_size / GMM_CHUNK_SIZE;
+	addr_t const unused_count = MAX_CHUNK_IDS - unused_id - 1;
+	chunk_ids.reserve(unused_id, unused_count);
+
 	return vm_memory;
 }
 
@@ -156,7 +170,7 @@ HRESULT genode_setup_machine(ComObjPtr<Machine> machine)
 	HRESULT ret = genode_check_memory_config(machine);
 
 	if (ret == VINF_SUCCESS)
-		vm_memory(memory_vbox * 1024 * 1024 + (CHUNKID_START + 1) * GMM_CHUNK_SIZE);
+		vm_memory(1024ULL * 1024 * memory_vbox + (CHUNKID_START + 1) * GMM_CHUNK_SIZE);
 
 	return ret;
 };
@@ -307,17 +321,6 @@ int SUPR3CallVMMR0Ex(PVMR0 pVMR0, VMCPUID idCpu, unsigned uOperation,
 		GVMMCREATEVMREQ &req = reinterpret_cast<GVMMCREATEVMREQ &>(*pReqHdr);
 		SUPR3QueryHWACCLonGenodeSupport(reinterpret_cast<VM *>(req.pVMR3));
 
-		/* reserve lower chunk ids */
-		try {
-			for (unsigned i = 0; i < CHUNKID_START; i++) {
-				unsigned chunkid = chunk_ids.alloc();
-				AssertMsg(chunkid == i, ("chunkid %u != %u i\n", chunkid, i));
-			}
-		} catch (...) {
-			Genode::error(__func__," ", __LINE__, " allocation failed");
-			throw;
-		}
-
 		return VINF_SUCCESS;
 	}
 	case VMMR0_DO_GVMM_REGISTER_VMCPU:
@@ -443,7 +446,7 @@ int SUPR3CallVMMR0Ex(PVMR0 pVMR0, VMCPUID idCpu, unsigned uOperation,
 		Assert(req->idChunkUnmap == NIL_GMM_CHUNKID);
 		Assert(req->idChunkMap   != NIL_GMM_CHUNKID);
 
-		Genode::addr_t local_addr_offset = req->idChunkMap << GMM_CHUNK_SHIFT;
+		Genode::addr_t local_addr_offset = (uintptr_t)req->idChunkMap << GMM_CHUNK_SHIFT;
 		Genode::addr_t to = vm_memory().local_addr(local_addr_offset);
 
 		req->pvR3 = reinterpret_cast<RTR3PTR>(to);
@@ -501,7 +504,7 @@ int SUPR3CallVMMR0Ex(PVMR0 pVMR0, VMCPUID idCpu, unsigned uOperation,
 			AssertMsgReturn(pVM->pgm.s.aHandyPages[iFirst + iPage].idSharedPage == NIL_GMM_PAGEID, ("#%#x: %#x\n", iFirst + iPage, pVM->pgm.s.aHandyPages[iFirst + iPage].idSharedPage),  VERR_INVALID_PARAMETER);
 		}
 
-		unsigned chunkid = 0;
+		Genode::uint64_t chunkid = 0;
 
 		try {
 			chunkid = chunk_ids.alloc();
@@ -576,7 +579,7 @@ int SUPR3CallVMMR0Ex(PVMR0 pVMR0, VMCPUID idCpu, unsigned uOperation,
 		Assert(pVM->pgm.s.cLargeHandyPages == 0);
 
 		try {
-			unsigned chunkid = chunk_ids.alloc();
+			Genode::uint64_t chunkid = chunk_ids.alloc();
 
 			pVM->pgm.s.aLargeHandyPage[0].idPage = (chunkid << GMM_CHUNKID_SHIFT);
 			pVM->pgm.s.aLargeHandyPage[0].HCPhysGCPhys = vm_memory().local_addr(chunkid << GMM_CHUNK_SHIFT);