diff --git a/lib/glacier/status/error.h b/lib/glacier/status/error.h
index 95229d3..d8cbc78 100644
--- a/lib/glacier/status/error.h
+++ b/lib/glacier/status/error.h
@@ -4,37 +4,37 @@
 
 namespace glcr {
 
-typedef uint64_t ErrorCode;
+enum ErrorCode : uint64_t {
+  OK = 0x0,
+  // First set of error codes generally indicate user errors.
+  INVALID_ARGUMENT = 0x1,
+  NOT_FOUND = 0x2,
+  PERMISSION_DENIED = 0x3,
+  NULL_PTR = 0x4,
+  EMPTY = 0x5,
+  ALREADY_EXISTS = 0x6,
+  BUFFER_SIZE = 0x7,
+  FAILED_PRECONDITION = 0x8,
 
-#define RET_ERR(expr)           \
-  {                             \
-    z_err_t _tmp_err = expr;    \
-    if (_tmp_err != glcr::OK) { \
-      return _tmp_err;          \
-    }                           \
+  // Second set of error codes generally indicate service errors.
+  INTERNAL = 0x100,
+  UNIMPLEMENTED = 0x101,
+  EXHAUSTED = 0x102,
+  INVALID_RESPONSE = 0x103,
+
+  // Kernel specific error codes (relating to capabilities).
+  CAP_NOT_FOUND = 0x1000,
+  CAP_WRONG_TYPE = 0x1001,
+  CAP_PERMISSION_DENIED = 0x1002,
+
+};
+
+#define RET_ERR(expr)                                              \
+  {                                                                \
+    glcr::ErrorCode _tmp_err = static_cast<glcr::ErrorCode>(expr); \
+    if (_tmp_err != glcr::OK) {                                    \
+      return _tmp_err;                                             \
+    }                                                              \
   }
 
-static const uint64_t OK = 0x0;
-
-// First set of error codes generally indicate user errors.
-static const uint64_t INVALID_ARGUMENT = 0x1;
-static const uint64_t NOT_FOUND = 0x2;
-static const uint64_t PERMISSION_DENIED = 0x3;
-static const uint64_t NULL_PTR = 0x4;
-static const uint64_t EMPTY = 0x5;
-static const uint64_t ALREADY_EXISTS = 0x6;
-static const uint64_t BUFFER_SIZE = 0x7;
-static const uint64_t FAILED_PRECONDITION = 0x8;
-
-// Second set of error codes generally indicate service errors.
-static const uint64_t INTERNAL = 0x100;
-static const uint64_t UNIMPLEMENTED = 0x101;
-static const uint64_t EXHAUSTED = 0x102;
-static const uint64_t INVALID_RESPONSE = 0x103;
-
-// Kernel specific error codes (relating to capabilities).
-static const uint64_t CAP_NOT_FOUND = 0x1000;
-static const uint64_t CAP_WRONG_TYPE = 0x1001;
-static const uint64_t CAP_PERMISSION_DENIED = 0x1002;
-
 }  // namespace glcr
diff --git a/lib/mammoth/include/mammoth/response_context.h b/lib/mammoth/include/mammoth/response_context.h
index fbd0d2a..da5fcb1 100644
--- a/lib/mammoth/include/mammoth/response_context.h
+++ b/lib/mammoth/include/mammoth/response_context.h
@@ -29,7 +29,8 @@ class ResponseContext {
         code,
     };
     written_ = true;
-    return ZReplyPortSend(reply_port_, sizeof(response), &response, 0, nullptr);
+    return static_cast<glcr::ErrorCode>(
+        ZReplyPortSend(reply_port_, sizeof(response), &response, 0, nullptr));
   }
 
   bool HasWritten() { return written_; }
diff --git a/lib/mammoth/src/endpoint_server.cpp b/lib/mammoth/src/endpoint_server.cpp
index aa5a4c3..9e67cb6 100644
--- a/lib/mammoth/src/endpoint_server.cpp
+++ b/lib/mammoth/src/endpoint_server.cpp
@@ -23,9 +23,9 @@ void EndpointServer::ServerThread() {
     uint64_t message_size = kBufferSize;
     uint64_t reply_port_cap = 0;
     uint64_t num_caps = 0;
-    glcr::ErrorCode err =
+    glcr::ErrorCode err = static_cast<glcr::ErrorCode>(
         ZEndpointRecv(endpoint_cap_, &message_size, recieve_buffer_, &num_caps,
-                      nullptr, &reply_port_cap);
+                      nullptr, &reply_port_cap));
     if (err != glcr::OK) {
       dbgln("Error in receive: %x", err);
       continue;
diff --git a/lib/mammoth/src/mutex.cpp b/lib/mammoth/src/mutex.cpp
index cca7223..dd49ce5 100644
--- a/lib/mammoth/src/mutex.cpp
+++ b/lib/mammoth/src/mutex.cpp
@@ -19,5 +19,9 @@ glcr::ErrorOr<Mutex> Mutex::Create() {
   return Mutex(mutex_cap);
 }
 
-glcr::ErrorCode Mutex::Lock() { return ZMutexLock(mutex_cap_); }
-glcr::ErrorCode Mutex::Release() { return ZMutexRelease(mutex_cap_); }
+glcr::ErrorCode Mutex::Lock() {
+  return static_cast<glcr::ErrorCode>(ZMutexLock(mutex_cap_));
+}
+glcr::ErrorCode Mutex::Release() {
+  return static_cast<glcr::ErrorCode>(ZMutexRelease(mutex_cap_));
+}
diff --git a/lib/mammoth/src/port_client.cpp b/lib/mammoth/src/port_client.cpp
index 64b2820..61ef1ef 100644
--- a/lib/mammoth/src/port_client.cpp
+++ b/lib/mammoth/src/port_client.cpp
@@ -9,5 +9,6 @@ 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);
+  return static_cast<glcr::ErrorCode>(
+      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 13c0e83..c684104 100644
--- a/lib/mammoth/src/port_server.cpp
+++ b/lib/mammoth/src/port_server.cpp
@@ -31,7 +31,7 @@ glcr::ErrorCode PortServer::RecvCap(uint64_t *num_bytes, char *msg,
   return glcr::OK;
 }
 
-z_err_t PortServer::PollForIntCap(uint64_t *msg, uint64_t *cap) {
+glcr::ErrorCode PortServer::PollForIntCap(uint64_t *msg, uint64_t *cap) {
   uint64_t bytes = sizeof(uint64_t);
   uint64_t caps = 1;
   RET_ERR(ZPortPoll(port_cap_, &bytes, reinterpret_cast<uint8_t *>(msg), &caps,
diff --git a/lib/mammoth/src/thread.cpp b/lib/mammoth/src/thread.cpp
index 333f5ea..2d3eb8c 100644
--- a/lib/mammoth/src/thread.cpp
+++ b/lib/mammoth/src/thread.cpp
@@ -22,4 +22,6 @@ Thread::Thread(Entry e, const void* arg1) {
                      reinterpret_cast<uint64_t>(arg1)));
 }
 
-glcr::ErrorCode Thread::Join() { return ZThreadWait(thread_cap_); }
+glcr::ErrorCode Thread::Join() {
+  return static_cast<glcr::ErrorCode>(ZThreadWait(thread_cap_));
+}
diff --git a/sys/denali/lib/denali/denali.yunq.server.cpp b/sys/denali/lib/denali/denali.yunq.server.cpp
index 8d85e29..3e523da 100644
--- a/sys/denali/lib/denali/denali.yunq.server.cpp
+++ b/sys/denali/lib/denali/denali.yunq.server.cpp
@@ -51,7 +51,7 @@ void DenaliServerBase::ServerThread() {
     uint64_t recv_cap_size = 0x10;
     uint64_t recv_buf_size = 0x1000;
     recv_cap.Reset();
-    glcr::ErrorCode recv_err = ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap);
+    glcr::ErrorCode recv_err = static_cast<glcr::ErrorCode>(ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap));
     if (recv_err != glcr::OK) {
       dbgln("Error in receive: %x", recv_err);
       continue;
@@ -64,10 +64,10 @@ void DenaliServerBase::ServerThread() {
     glcr::ErrorCode err = HandleRequest(recv_buffer, recv_cap, resp_buffer, resp_length, resp_cap);
     if (err != glcr::OK) {
       WriteError(resp_buffer, err);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr);
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr));
     } else {
       WriteHeader(resp_buffer, resp_length);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr());
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr()));
     }
     if (reply_err != glcr::OK) {
       dbgln("Error in reply: %x", reply_err);
diff --git a/sys/victoriafalls/lib/victoriafalls/victoriafalls.yunq.server.cpp b/sys/victoriafalls/lib/victoriafalls/victoriafalls.yunq.server.cpp
index aa537ef..eea064d 100644
--- a/sys/victoriafalls/lib/victoriafalls/victoriafalls.yunq.server.cpp
+++ b/sys/victoriafalls/lib/victoriafalls/victoriafalls.yunq.server.cpp
@@ -51,7 +51,7 @@ void VFSServerBase::ServerThread() {
     uint64_t recv_cap_size = 0x10;
     uint64_t recv_buf_size = 0x1000;
     recv_cap.Reset();
-    glcr::ErrorCode recv_err = ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap);
+    glcr::ErrorCode recv_err = static_cast<glcr::ErrorCode>(ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap));
     if (recv_err != glcr::OK) {
       dbgln("Error in receive: %x", recv_err);
       continue;
@@ -64,10 +64,10 @@ void VFSServerBase::ServerThread() {
     glcr::ErrorCode err = HandleRequest(recv_buffer, recv_cap, resp_buffer, resp_length, resp_cap);
     if (err != glcr::OK) {
       WriteError(resp_buffer, err);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr);
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr));
     } else {
       WriteHeader(resp_buffer, resp_length);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr());
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr()));
     }
     if (reply_err != glcr::OK) {
       dbgln("Error in reply: %x", reply_err);
diff --git a/sys/yellowstone/lib/yellowstone/yellowstone.yunq.server.cpp b/sys/yellowstone/lib/yellowstone/yellowstone.yunq.server.cpp
index 708c15b..ffa25aa 100644
--- a/sys/yellowstone/lib/yellowstone/yellowstone.yunq.server.cpp
+++ b/sys/yellowstone/lib/yellowstone/yellowstone.yunq.server.cpp
@@ -51,7 +51,7 @@ void YellowstoneServerBase::ServerThread() {
     uint64_t recv_cap_size = 0x10;
     uint64_t recv_buf_size = 0x1000;
     recv_cap.Reset();
-    glcr::ErrorCode recv_err = ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap);
+    glcr::ErrorCode recv_err = static_cast<glcr::ErrorCode>(ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap));
     if (recv_err != glcr::OK) {
       dbgln("Error in receive: %x", recv_err);
       continue;
@@ -64,10 +64,10 @@ void YellowstoneServerBase::ServerThread() {
     glcr::ErrorCode err = HandleRequest(recv_buffer, recv_cap, resp_buffer, resp_length, resp_cap);
     if (err != glcr::OK) {
       WriteError(resp_buffer, err);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr);
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr));
     } else {
       WriteHeader(resp_buffer, resp_length);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr());
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr()));
     }
     if (reply_err != glcr::OK) {
       dbgln("Error in reply: %x", reply_err);
diff --git a/yunq/server.cpp.jinja b/yunq/server.cpp.jinja
index c299c04..590027d 100644
--- a/yunq/server.cpp.jinja
+++ b/yunq/server.cpp.jinja
@@ -51,7 +51,7 @@ void {{interface.name}}ServerBase::ServerThread() {
     uint64_t recv_cap_size = 0x10;
     uint64_t recv_buf_size = 0x1000;
     recv_cap.Reset();
-    glcr::ErrorCode recv_err = ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap);
+    glcr::ErrorCode recv_err = static_cast<glcr::ErrorCode>(ZEndpointRecv(endpoint_, &recv_buf_size, recv_buffer.RawPtr(), &recv_cap_size, recv_cap.RawPtr(), &reply_port_cap));
     if (recv_err != glcr::OK) {
       dbgln("Error in receive: %x", recv_err);
       continue;
@@ -64,10 +64,10 @@ void {{interface.name}}ServerBase::ServerThread() {
     glcr::ErrorCode err = HandleRequest(recv_buffer, recv_cap, resp_buffer, resp_length, resp_cap);
     if (err != glcr::OK) {
       WriteError(resp_buffer, err);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr);
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize, resp_buffer.RawPtr(), 0, nullptr));
     } else {
       WriteHeader(resp_buffer, resp_length);
-      reply_err = ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr());
+      reply_err = static_cast<glcr::ErrorCode>(ZReplyPortSend(reply_port_cap, kHeaderSize + resp_length, resp_buffer.RawPtr(), resp_cap.UsedSlots(), resp_cap.RawPtr()));
     }
     if (reply_err != glcr::OK) {
       dbgln("Error in reply: %x", reply_err);
diff --git a/zion/capability/capability.h b/zion/capability/capability.h
index 8f2c7fc..6a20183 100644
--- a/zion/capability/capability.h
+++ b/zion/capability/capability.h
@@ -48,8 +48,8 @@ glcr::RefPtr<T> Capability::obj() {
 }
 
 template <typename T>
-z_err_t ValidateCapability(const glcr::RefPtr<Capability>& cap,
-                           uint64_t permissions) {
+glcr::ErrorCode ValidateCapability(const glcr::RefPtr<Capability>& cap,
+                                   uint64_t permissions) {
   if (!cap) {
     return glcr::CAP_NOT_FOUND;
   }
diff --git a/zion/lib/message_queue.cpp b/zion/lib/message_queue.cpp
index 5588ecf..9b3340c 100644
--- a/zion/lib/message_queue.cpp
+++ b/zion/lib/message_queue.cpp
@@ -3,9 +3,11 @@
 #include "debug/debug.h"
 #include "scheduler/scheduler.h"
 
-z_err_t UnboundedMessageQueue::PushBack(uint64_t num_bytes, const void* bytes,
-                                        uint64_t num_caps, const z_cap_t* caps,
-                                        z_cap_t reply_cap) {
+glcr::ErrorCode UnboundedMessageQueue::PushBack(uint64_t num_bytes,
+                                                const void* bytes,
+                                                uint64_t num_caps,
+                                                const z_cap_t* caps,
+                                                z_cap_t reply_cap) {
   if (num_bytes > 0x1000) {
     dbgln("Large message size unimplemented: %x", num_bytes);
     return glcr::UNIMPLEMENTED;
@@ -51,9 +53,10 @@ z_err_t UnboundedMessageQueue::PushBack(uint64_t num_bytes, const void* bytes,
   return glcr::OK;
 }
 
-z_err_t UnboundedMessageQueue::PopFront(uint64_t* num_bytes, void* bytes,
-                                        uint64_t* num_caps, z_cap_t* caps,
-                                        z_cap_t* reply_cap) {
+glcr::ErrorCode UnboundedMessageQueue::PopFront(uint64_t* num_bytes,
+                                                void* bytes, uint64_t* num_caps,
+                                                z_cap_t* caps,
+                                                z_cap_t* reply_cap) {
   mutex_->Lock();
   while (pending_messages_.empty()) {
     auto thread = gScheduler->CurrentThread();
diff --git a/zion/syscall/ipc.cpp b/zion/syscall/ipc.cpp
index e4d853c..f876825 100644
--- a/zion/syscall/ipc.cpp
+++ b/zion/syscall/ipc.cpp
@@ -6,7 +6,7 @@
 #include "object/reply_port.h"
 #include "scheduler/scheduler.h"
 
-z_err_t ChannelCreate(ZChannelCreateReq* req) {
+glcr::ErrorCode ChannelCreate(ZChannelCreateReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   auto chan_pair = Channel::CreateChannelPair();
   *req->channel1 = proc.AddNewCapability(chan_pair.first());
@@ -14,7 +14,7 @@ z_err_t ChannelCreate(ZChannelCreateReq* req) {
   return glcr::OK;
 }
 
-z_err_t ChannelSend(ZChannelSendReq* req) {
+glcr::ErrorCode ChannelSend(ZChannelSendReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   auto chan_cap = proc.GetCapability(req->chan_cap);
   RET_ERR(ValidateCapability<Channel>(chan_cap, kZionPerm_Write));
@@ -23,7 +23,7 @@ z_err_t ChannelSend(ZChannelSendReq* req) {
   return chan->Send(req->num_bytes, req->data, req->num_caps, req->caps);
 }
 
-z_err_t ChannelRecv(ZChannelRecvReq* req) {
+glcr::ErrorCode ChannelRecv(ZChannelRecvReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   auto chan_cap = proc.GetCapability(req->chan_cap);
   RET_ERR(ValidateCapability<Channel>(chan_cap, kZionPerm_Read));
@@ -32,14 +32,14 @@ z_err_t ChannelRecv(ZChannelRecvReq* req) {
   return chan->Recv(req->num_bytes, req->data, req->num_caps, req->caps);
 }
 
-z_err_t PortCreate(ZPortCreateReq* req) {
+glcr::ErrorCode PortCreate(ZPortCreateReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   auto port = glcr::MakeRefCounted<Port>();
   *req->port_cap = proc.AddNewCapability(port);
   return glcr::OK;
 }
 
-z_err_t PortSend(ZPortSendReq* req) {
+glcr::ErrorCode PortSend(ZPortSendReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   auto port_cap = proc.GetCapability(req->port_cap);
   RET_ERR(ValidateCapability<Port>(port_cap, kZionPerm_Write));
@@ -48,7 +48,7 @@ z_err_t PortSend(ZPortSendReq* req) {
   return port->Send(req->num_bytes, req->data, req->num_caps, req->caps);
 }
 
-z_err_t PortRecv(ZPortRecvReq* req) {
+glcr::ErrorCode PortRecv(ZPortRecvReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   auto port_cap = proc.GetCapability(req->port_cap);
   RET_ERR(ValidateCapability<Port>(port_cap, kZionPerm_Read));
@@ -63,7 +63,7 @@ z_err_t PortRecv(ZPortRecvReq* req) {
   return port->Recv(req->num_bytes, req->data, req->num_caps, req->caps);
 }
 
-z_err_t PortPoll(ZPortPollReq* req) {
+glcr::ErrorCode PortPoll(ZPortPollReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   auto port_cap = proc.GetCapability(req->port_cap);
   RET_ERR(ValidateCapability<Port>(port_cap, kZionPerm_Read));
@@ -77,7 +77,7 @@ z_err_t PortPoll(ZPortPollReq* req) {
   return port->Recv(req->num_bytes, req->data, req->num_caps, req->caps);
 }
 
-z_err_t IrqRegister(ZIrqRegisterReq* req) {
+glcr::ErrorCode IrqRegister(ZIrqRegisterReq* req) {
   auto& proc = gScheduler->CurrentProcess();
   if (req->irq_num != Z_IRQ_PCI_BASE) {
     // FIXME: Don't hardcode this nonsense.