diff --git a/src/dataencode.cpp b/src/dataencode.cpp
index 365149b..34212cd 100644
--- a/src/dataencode.cpp
+++ b/src/dataencode.cpp
@@ -432,16 +432,17 @@ void to_wire_full(Buffer& buf, const Value& val)
     to_wire_field(buf, Value::Helper::desc(val), Value::Helper::store(val));
 }
 
-void to_wire_valid(Buffer& buf, const Value& val)
+void to_wire_valid(Buffer& buf, const Value& val, const BitMask* mask)
 {
     auto desc = Value::Helper::desc(val);
     auto store = Value::Helper::store(val);
     assert(desc && desc->code==TypeCode::Struct);
+    assert(!mask || mask->size()==desc->size());
 
     BitMask valid(desc->size());
 
     for(auto bit : range(desc->size())) {
-        if((store.get()+bit)->valid)
+        if((store.get()+bit)->valid && (!mask || (*mask)[bit]))
             valid[bit] = true;
     }
 
diff --git a/src/dataimpl.h b/src/dataimpl.h
index df7ce37..59d1878 100644
--- a/src/dataimpl.h
+++ b/src/dataimpl.h
@@ -147,18 +147,23 @@ struct StructTop {
 using Type = std::shared_ptr<const FieldDesc>;
 
 
+//! serialize all Value fields
 PVXS_API
 void to_wire_full(Buffer& buf, const Value& val);
 
+//! serialize BitMask and marked valid Value fields
 PVXS_API
-void to_wire_valid(Buffer& buf, const Value& val);
+void to_wire_valid(Buffer& buf, const Value& val, const BitMask* mask=nullptr);
 
+//! deserialize type description
 PVXS_API
 void from_wire_full(Buffer& buf, TypeStore& ctxt, Value& val);
 
+//! deserialize BitMask and partial Value
 PVXS_API
 void from_wire_valid(Buffer& buf, TypeStore& ctxt, Value& val);
 
+//! deserialize type description and full value (a la. pvRequest)
 PVXS_API
 void from_wire_type_value(Buffer& buf, TypeStore& ctxt, Value& val);
 
diff --git a/src/serverget.cpp b/src/serverget.cpp
index 5bc90de..67e06f8 100644
--- a/src/serverget.cpp
+++ b/src/serverget.cpp
@@ -9,6 +9,7 @@
 #include <pvxs/log.h>
 #include "dataimpl.h"
 #include "serverconn.h"
+#include "pvrequest.h"
 
 namespace pvxs { namespace impl {
 DEFINE_LOGGER(connsetup, "pvxs.tcp.setup");
@@ -24,8 +25,7 @@ struct ServerGPR : public ServerOp
     {}
     virtual ~ServerGPR() {}
 
-    void doReply(const std::shared_ptr<const FieldDesc>& type,
-                 const Value& value,
+    void doReply(const Value& value,
                  const std::string& msg)
     {
         auto ch = chan.lock();
@@ -38,12 +38,13 @@ struct ServerGPR : public ServerOp
         if(state==Dead || state==Idle) {
             // no warn if Idle as this may result from a remote Cancel
             return;
-        }
 
-        if(type && this->type)
-            throw std::logic_error("Operation already connected (has a type)");
-        if(cmd!=CMD_PUT && this->type && (!value || Value::Helper::desc(value)!=this->type.get()))
-            throw std::logic_error("PUT Must reply with exact type previously passed to connect()");
+        } else if(state==Executing) {
+            if(cmd==CMD_PUT && !value)
+                throw std::logic_error("PUT reply can't include Value");
+            else if(cmd==CMD_GET && this->type && (!value || Value::Helper::desc(value)!=this->type.get()))
+                throw std::logic_error("GET must reply with exact type previously passed to connect()");
+        }
 
         Status sts{};
         if(!msg.empty())
@@ -68,14 +69,13 @@ struct ServerGPR : public ServerOp
             } else if(state==Creating) {
                 // connect()
                 if(cmd!=CMD_RPC) {
-                    this->type = type;
                     to_wire(R, type.get());
                 }
                 state = Idle;
 
             } else if(state==Executing) {
                 if(cmd==CMD_GET || (cmd==CMD_PUT && (subcmd&0x40))) {
-                    to_wire_valid(R, value); // GET and PUT/Get reply with bitmask and partial value
+                    to_wire_valid(R, value, &pvMask); // GET and PUT/Get reply with bitmask and partial value
 
                 } else if(cmd==CMD_RPC) {
                     auto type = Value::Helper::desc(value);
@@ -117,6 +117,7 @@ struct ServerGPR : public ServerOp
     bool lastRequest=false;
 
     std::shared_ptr<const FieldDesc> type;
+    BitMask pvMask; // mask computed from pvRequest .fields
 
     std::function<void(const std::string&)> onClose;
     std::function<void(std::unique_ptr<server::ExecOp>&&, Value&&)> onPut;
@@ -158,11 +159,15 @@ struct ServerGPRConnect : public server::ConnectOp
                 if(!prototype && oper->cmd!=CMD_RPC)
                     throw std::invalid_argument("Must provide prototype");
 
-                std::shared_ptr<const FieldDesc> type;
-                if(prototype)
-                    type = Value::Helper::type(prototype);
+                if(oper->type)
+                    throw std::logic_error("Operation already connected (has a type)");
 
-                oper->doReply(type, Value(), std::string());
+                if(prototype) {
+                    oper->type = Value::Helper::type(prototype);
+                    oper->pvMask = request2mask(oper->type.get(), _pvRequest);
+                }
+
+                oper->doReply(Value(), std::string());
             }
         });
     }
@@ -176,7 +181,7 @@ struct ServerGPRConnect : public server::ConnectOp
         serv->acceptor_loop.call([this, &msg](){
             if(auto oper = op.lock()) {
                 if(oper->state==ServerOp::Creating)
-                    oper->doReply(nullptr, Value(), msg);
+                    oper->doReply(Value(), msg);
             }
         });
     }
@@ -245,7 +250,7 @@ struct ServerGPRExec : public server::ExecOp
             return;
         serv->acceptor_loop.call([this, &val](){
             if(auto oper = op.lock()) {
-                oper->doReply(nullptr, val, std::string());
+                oper->doReply(val, std::string());
             }
         });
     }
@@ -259,7 +264,7 @@ struct ServerGPRExec : public server::ExecOp
             return;
         serv->acceptor_loop.call([this, &msg](){
             if(auto oper = op.lock()) {
-                oper->doReply(nullptr, Value(), msg);
+                oper->doReply(Value(), msg);
             }
         });
     }