diff --git a/lib/mammoth/CMakeLists.txt b/lib/mammoth/CMakeLists.txt
index b25e601..f462f82 100644
--- a/lib/mammoth/CMakeLists.txt
+++ b/lib/mammoth/CMakeLists.txt
@@ -7,7 +7,7 @@ add_library(mammoth_lib STATIC
   src/memory_region.cpp
   src/new.cpp
   src/process.cpp
-  src/port.cpp
+  src/port_client.cpp
   src/port_server.cpp
   src/thread.cpp
   )
diff --git a/lib/mammoth/include/mammoth/port.h b/lib/mammoth/include/mammoth/port.h
deleted file mode 100644
index 4e64d60..0000000
--- a/lib/mammoth/include/mammoth/port.h
+++ /dev/null
@@ -1,26 +0,0 @@
-#pragma once
-
-#include <glacier/status/error_or.h>
-#include <glacier/string/string.h>
-#include <stdint.h>
-#include <zcall.h>
-
-// FIXME: Split send and receive.
-class Port {
- public:
-  static glcr::ErrorOr<Port> Create();
-  Port(uint64_t port_cap);
-
-  template <typename T>
-  z_err_t WriteMessage(const T& obj, uint64_t cap);
-
-  glcr::ErrorCode WriteString(glcr::String str, uint64_t cap);
-
- private:
-  uint64_t port_cap_;
-};
-
-template <typename T>
-z_err_t Port::WriteMessage(const T& obj, uint64_t cap) {
-  return ZPortSend(port_cap_, sizeof(obj), &obj, 1, &cap);
-}
diff --git a/lib/mammoth/include/mammoth/port_client.h b/lib/mammoth/include/mammoth/port_client.h
new file mode 100644
index 0000000..5f33db6
--- /dev/null
+++ b/lib/mammoth/include/mammoth/port_client.h
@@ -0,0 +1,28 @@
+#pragma once
+
+#include <glacier/status/error_or.h>
+#include <glacier/string/string.h>
+#include <stdint.h>
+#include <zcall.h>
+
+class PortClient {
+ public:
+  static PortClient AdoptPort(z_cap_t port_cap);
+
+  template <typename T>
+  z_err_t WriteMessage(const T& obj, z_cap_t cap);
+
+  glcr::ErrorCode WriteString(glcr::String str, z_cap_t cap);
+
+  z_cap_t cap() { return port_cap_; }
+
+ private:
+  z_cap_t port_cap_;
+
+  PortClient(z_cap_t port_cap);
+};
+
+template <typename T>
+z_err_t PortClient::WriteMessage(const T& obj, z_cap_t cap) {
+  return ZPortSend(port_cap_, sizeof(obj), &obj, 1, &cap);
+}
diff --git a/lib/mammoth/include/mammoth/port_server.h b/lib/mammoth/include/mammoth/port_server.h
index 1cc783a..e8939e4 100644
--- a/lib/mammoth/include/mammoth/port_server.h
+++ b/lib/mammoth/include/mammoth/port_server.h
@@ -3,16 +3,20 @@
 #include <glacier/status/error_or.h>
 #include <ztypes.h>
 
+#include "mammoth/port_client.h"
+
 class PortServer {
  public:
   static glcr::ErrorOr<PortServer> Create();
   static PortServer AdoptCap(z_cap_t cap);
 
-  glcr::ErrorCode CreateClient(z_cap_t* new_port);
+  glcr::ErrorOr<PortClient> CreateClient();
 
   glcr::ErrorCode RecvCap(uint64_t* num_bytes, char* msg, uint64_t* cap);
   glcr::ErrorCode PollForIntCap(uint64_t* msg, uint64_t* cap);
 
+  z_cap_t cap() { return port_cap_; }
+
  private:
   z_cap_t port_cap_;
 
diff --git a/lib/mammoth/src/port.cpp b/lib/mammoth/src/port.cpp
deleted file mode 100644
index b810cde..0000000
--- a/lib/mammoth/src/port.cpp
+++ /dev/null
@@ -1,17 +0,0 @@
-#include "mammoth/port.h"
-
-#include <glacier/status/error.h>
-#include <zcall.h>
-
-#include "mammoth/debug.h"
-
-glcr::ErrorOr<Port> Port::Create() {
-  z_cap_t port;
-  RET_ERR(ZPortCreate(&port));
-  return Port(port);
-}
-Port::Port(uint64_t port_cap) : port_cap_(port_cap) {}
-
-glcr::ErrorCode Port::WriteString(glcr::String str, uint64_t cap) {
-  return ZPortSend(port_cap_, str.length() + 1, str.cstr(), 1, &cap);
-}
diff --git a/lib/mammoth/src/port_client.cpp b/lib/mammoth/src/port_client.cpp
new file mode 100644
index 0000000..64b2820
--- /dev/null
+++ b/lib/mammoth/src/port_client.cpp
@@ -0,0 +1,13 @@
+#include "mammoth/port_client.h"
+
+#include <glacier/status/error.h>
+#include <zcall.h>
+
+#include "mammoth/debug.h"
+
+PortClient PortClient::AdoptPort(z_cap_t cap) { return PortClient(cap); }
+PortClient::PortClient(z_cap_t port_cap) : port_cap_(port_cap) {}
+
+glcr::ErrorCode PortClient::WriteString(glcr::String str, z_cap_t cap) {
+  return ZPortSend(port_cap_, str.length() + 1, str.cstr(), 1, &cap);
+}
diff --git a/lib/mammoth/src/port_server.cpp b/lib/mammoth/src/port_server.cpp
index 9de44c8..13c0e83 100644
--- a/lib/mammoth/src/port_server.cpp
+++ b/lib/mammoth/src/port_server.cpp
@@ -12,9 +12,11 @@ PortServer PortServer::AdoptCap(z_cap_t cap) { return PortServer(cap); }
 
 PortServer::PortServer(z_cap_t port_cap) : port_cap_(port_cap) {}
 
-glcr::ErrorCode PortServer::CreateClient(z_cap_t *new_port) {
+glcr::ErrorOr<PortClient> PortServer::CreateClient() {
   // FIXME: Restrict permissions.
-  return ZCapDuplicate(port_cap_, new_port);
+  z_cap_t new_port;
+  RET_ERR(ZCapDuplicate(port_cap_, &new_port));
+  return PortClient::AdoptPort(new_port);
 }
 
 glcr::ErrorCode PortServer::RecvCap(uint64_t *num_bytes, char *msg,
diff --git a/lib/mammoth/src/process.cpp b/lib/mammoth/src/process.cpp
index 0578442..a238279 100644
--- a/lib/mammoth/src/process.cpp
+++ b/lib/mammoth/src/process.cpp
@@ -6,7 +6,8 @@
 #include "mammoth/debug.h"
 #include "mammoth/endpoint_server.h"
 #include "mammoth/init.h"
-#include "mammoth/port.h"
+#include "mammoth/port_client.h"
+#include "mammoth/port_server.h"
 
 #define MAM_PROC_DEBUG 0
 
@@ -105,14 +106,13 @@ glcr::ErrorCode SpawnProcessFromElfRegion(uint64_t program,
 #if MAM_PROC_DEBUG
   dbgln("Port Create");
 #endif
-  RET_ERR(ZPortCreate(&port_cap));
-  uint64_t port_cap_donate;
-  RET_ERR(ZCapDuplicate(port_cap, &port_cap_donate));
+  ASSIGN_OR_RETURN(PortServer server, PortServer::Create());
+  ASSIGN_OR_RETURN(PortClient pclient, server.CreateClient());
 
 #if MAM_PROC_DEBUG
   dbgln("Spawn");
 #endif
-  RET_ERR(ZProcessSpawn(gSelfProcCap, port_cap_donate, &proc_cap, &as_cap,
+  RET_ERR(ZProcessSpawn(gSelfProcCap, server.cap(), &proc_cap, &as_cap,
                         &foreign_port_id));
 
   uint64_t entry_point = LoadElfProgram(program, as_cap);
@@ -123,10 +123,9 @@ glcr::ErrorCode SpawnProcessFromElfRegion(uint64_t program,
   uint64_t thread_cap;
   RET_ERR(ZThreadCreate(proc_cap, &thread_cap));
 
-  Port p(port_cap);
-  RET_ERR(p.WriteMessage<uint64_t>(Z_INIT_SELF_PROC, proc_cap));
-  RET_ERR(p.WriteMessage<uint64_t>(Z_INIT_SELF_VMAS, as_cap));
-  RET_ERR(p.WriteMessage<uint64_t>(Z_INIT_ENDPOINT, client.GetCap()));
+  RET_ERR(pclient.WriteMessage<uint64_t>(Z_INIT_SELF_PROC, proc_cap));
+  RET_ERR(pclient.WriteMessage<uint64_t>(Z_INIT_SELF_VMAS, as_cap));
+  RET_ERR(pclient.WriteMessage<uint64_t>(Z_INIT_ENDPOINT, client.GetCap()));
 
 #if MAM_PROC_DEBUG
   dbgln("Thread start");
diff --git a/sys/denali/denali.cpp b/sys/denali/denali.cpp
index 5dce931..320159b 100644
--- a/sys/denali/denali.cpp
+++ b/sys/denali/denali.cpp
@@ -2,7 +2,7 @@
 #include <mammoth/debug.h>
 #include <mammoth/endpoint_server.h>
 #include <mammoth/init.h>
-#include <mammoth/port.h>
+#include <mammoth/port_client.h>
 #include <stdint.h>
 #include <yellowstone.h>
 
@@ -26,7 +26,7 @@ uint64_t main(uint64_t init_port_cap) {
     check(resp_cap_or.error());
   }
   auto resp_cap = resp_cap_or.value();
-  Port notify(resp_cap.second());
+  PortClient notify = PortClient::AdoptPort(resp_cap.second());
 
   ASSIGN_OR_RETURN(EndpointServer endpoint, EndpointServer::Create());
   ASSIGN_OR_RETURN(EndpointClient client, endpoint.CreateClient());
diff --git a/sys/yellowstone/yellowstone_server.cpp b/sys/yellowstone/yellowstone_server.cpp
index ab4580e..1e8e0cb 100644
--- a/sys/yellowstone/yellowstone_server.cpp
+++ b/sys/yellowstone/yellowstone_server.cpp
@@ -61,9 +61,12 @@ void YellowstoneServer::ServerThread() {
         break;
       case kYellowstoneGetRegistration: {
         dbgln("Yellowstone::GetRegistration");
-        uint64_t reg_cap;
-        check(register_port_.CreateClient(&reg_cap));
+        auto client_or = register_port_.CreateClient();
+        if (!client_or.ok()) {
+          check(client_or.error());
+        }
         YellowstoneGetRegistrationResp resp;
+        uint64_t reg_cap = client_or.value().cap();
         check(ZReplyPortSend(reply_port_cap, sizeof(resp), &resp, 1, &reg_cap));
         break;
       }