diff --git a/src/clientconn.cpp b/src/clientconn.cpp
index 2232166..437ecaa 100644
--- a/src/clientconn.cpp
+++ b/src/clientconn.cpp
@@ -15,7 +15,7 @@ namespace client {
 DEFINE_LOGGER(io, "pvxs.client.io");
 
 Connection::Connection(const std::shared_ptr<ContextImpl>& context, const SockAddr& peerAddr)
-    :ConnBase (true,
+    :ConnBase (true, context->effective.sendBE(),
                bufferevent_socket_new(context->tcp_loop.base, -1, BEV_OPT_CLOSE_ON_FREE|BEV_OPT_DEFER_CALLBACKS),
                peerAddr)
     ,context(context)
diff --git a/src/conn.cpp b/src/conn.cpp
index dfb28aa..c45d243 100644
--- a/src/conn.cpp
+++ b/src/conn.cpp
@@ -17,12 +17,12 @@ DEFINE_LOGGER(connio, "pvxs.tcp.io");
 namespace pvxs {
 namespace impl {
 
-ConnBase::ConnBase(bool isClient, bufferevent* bev, const SockAddr& peerAddr)
+ConnBase::ConnBase(bool isClient, bool sendBE, bufferevent* bev, const SockAddr& peerAddr)
     :peerAddr(peerAddr)
     ,peerName(peerAddr.tostring())
     ,bev(bev)
     ,isClient(isClient)
-    ,sendBE(EPICS_BYTE_ORDER==EPICS_ENDIAN_BIG)
+    ,sendBE(sendBE)
     ,peerBE(true) // arbitrary choice, default should be overwritten before use
     ,expectSeg(false)
     ,segCmd(0xff)
diff --git a/src/conn.h b/src/conn.h
index 5431d85..582989d 100644
--- a/src/conn.h
+++ b/src/conn.h
@@ -36,7 +36,7 @@ struct ConnBase
 
     size_t statTx{}, statRx{};
 
-    ConnBase(bool isClient, bufferevent* bev, const SockAddr& peerAddr);
+    ConnBase(bool isClient, bool sendBE, bufferevent* bev, const SockAddr& peerAddr);
     ConnBase(const ConnBase&) = delete;
     ConnBase& operator=(const ConnBase&) = delete;
     virtual ~ConnBase();
diff --git a/src/pvxs/client.h b/src/pvxs/client.h
index 56f6fa6..f87bf1a 100644
--- a/src/pvxs/client.h
+++ b/src/pvxs/client.h
@@ -16,6 +16,7 @@
 #include <typeinfo>
 
 #include <epicsTime.h>
+#include <epicsEndian.h>
 
 #include <pvxs/version.h>
 #include <pvxs/data.h>
@@ -971,6 +972,10 @@ struct PVXS_API Config {
     //! @since 0.2.0
     double tcpTimeout = 40.0;
 
+private:
+    bool BE = EPICS_BYTE_ORDER==EPICS_ENDIAN_BIG;
+public:
+
     // compat
     static inline Config from_env() { return Config{}.applyEnv(); }
 
@@ -1004,6 +1009,12 @@ struct PVXS_API Config {
     Context build() const {
         return Context(*this);
     }
+
+#ifdef PVXS_EXPERT_API_ENABLED
+    // for protocol compatibility testing
+    inline Config& overrideSendBE(bool be) { BE = be; return *this; }
+    inline bool sendBE() const { return BE; }
+#endif
 };
 
 PVXS_API
diff --git a/src/pvxs/server.h b/src/pvxs/server.h
index 948fe89..b3071fa 100644
--- a/src/pvxs/server.h
+++ b/src/pvxs/server.h
@@ -18,6 +18,8 @@
 #include <memory>
 #include <array>
 
+#include <epicsEndian.h>
+
 #include <pvxs/version.h>
 #include <pvxs/util.h>
 #include <pvxs/data.h>
@@ -172,6 +174,10 @@ struct PVXS_API Config {
     //! Server unique ID.  Only meaningful in readback via Server::config()
     ServerGUID guid{};
 
+private:
+    bool BE = EPICS_BYTE_ORDER==EPICS_ENDIAN_BIG;
+public:
+
     // compat
     static inline Config from_env() { return Config{}.applyEnv(); }
 
@@ -209,6 +215,12 @@ struct PVXS_API Config {
     inline Server build() const {
         return Server(*this);
     }
+
+#ifdef PVXS_EXPERT_API_ENABLED
+    // for protocol compatibility testing
+    inline Config& overrideSendBE(bool be) { BE = be; return *this; }
+    inline bool sendBE() const { return BE; }
+#endif
 };
 
 PVXS_API
diff --git a/src/serverconn.cpp b/src/serverconn.cpp
index 80d18a4..4e7c4ef 100644
--- a/src/serverconn.cpp
+++ b/src/serverconn.cpp
@@ -44,7 +44,7 @@ DEFINE_LOGGER(connio, "pvxs.tcp.io");
 DEFINE_LOGGER(remote, "pvxs.remote.log");
 
 ServerConn::ServerConn(ServIface* iface, evutil_socket_t sock, struct sockaddr *peer, int socklen)
-    :ConnBase(false,
+    :ConnBase(false, iface->server->effective.sendBE(),
               bufferevent_socket_new(iface->server->acceptor_loop.base, sock, BEV_OPT_CLOSE_ON_FREE|BEV_OPT_DEFER_CALLBACKS),
               SockAddr(peer))
     ,iface(iface)
diff --git a/test/Makefile b/test/Makefile
index 13ebb95..b51f28d 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -94,6 +94,10 @@ TESTPROD_HOST += test1000
 test1000_SRCS += test1000.cpp
 TESTS += test1000
 
+TESTPROD_HOST += testendian
+testendian_SRCS += testendian.cpp
+TESTS += testendian
+
 ifdef BASE_7_0
 
 TESTPROD_HOST += benchdata
diff --git a/test/testendian.cpp b/test/testendian.cpp
new file mode 100644
index 0000000..9846938
--- /dev/null
+++ b/test/testendian.cpp
@@ -0,0 +1,73 @@
+/**
+ * Copyright - See the COPYRIGHT that is included with this distribution.
+ * pvxs is distributed subject to a Software License Agreement found
+ * in file LICENSE that is included with this distribution.
+ */
+#define PVXS_ENABLE_EXPERT_API
+
+#include <testMain.h>
+
+#include <epicsUnitTest.h>
+
+#include <epicsEvent.h>
+
+#include <pvxs/unittest.h>
+#include <pvxs/log.h>
+#include <pvxs/client.h>
+#include <pvxs/server.h>
+#include <pvxs/sharedpv.h>
+#include <pvxs/source.h>
+#include <pvxs/nt.h>
+
+namespace {
+using namespace pvxs;
+
+void testEndian(bool srvBE, bool cliBE)
+{
+    testDiag("%s(%c, %c)", __func__,
+             srvBE ? 'B' : 'L',
+             cliBE ? 'B' : 'L');
+
+    const auto proto = nt::NTScalar{TypeCode::UInt32}
+            .create()
+            .update("value", 42);
+
+    auto mbox(server::SharedPV::buildMailbox());
+
+    mbox.open(proto);
+
+    auto srv = server::Config::isolated()
+            .overrideSendBE(srvBE)
+            .build()
+            .addPV("dut", mbox)
+            .start();
+
+    auto cli = srv.clientConfig()
+            .overrideSendBE(cliBE)
+            .build();
+
+    try {
+        auto val = cli.get("dut")
+                .exec()
+                ->wait(5.0);
+
+        testEq(val["value"].as<uint32_t>(), 42u);
+    }catch(std::exception& e){
+        testFail("Unexpected exception: %s\n", e.what());
+    }
+}
+
+} // namespace
+
+MAIN(testendian)
+{
+    testPlan(4);
+    testSetup();
+    logger_config_env();
+    testEndian(false, false);
+    testEndian(false, true);
+    testEndian(true, false);
+    testEndian(true, true);
+    cleanup_for_valgrind();
+    return testDone();
+}