diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 7d006f451..55ecab0ff 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -134,7 +134,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
 
             debug("querying remote host '%s' for info on '%s'", host, printStorePath(path));
 
-            conn->to << cmdQueryPathInfos << PathSet{printStorePath(path)};
+            conn->to << ServeProto::Command::QueryPathInfos << PathSet{printStorePath(path)};
             conn->to.flush();
 
             auto p = readString(conn->from);
@@ -177,7 +177,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 5) {
 
             conn->to
-                << cmdAddToStoreNar
+                << ServeProto::Command::AddToStoreNar
                 << printStorePath(info.path)
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << info.narHash.to_string(Base16, false);
@@ -199,7 +199,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
         } else {
 
             conn->to
-                << cmdImportPaths
+                << ServeProto::Command::ImportPaths
                 << 1;
             try {
                 copyNAR(source, conn->to);
@@ -227,7 +227,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
     {
         auto conn(connections->get());
 
-        conn->to << cmdDumpStorePath << printStorePath(path);
+        conn->to << ServeProto::Command::DumpStorePath << printStorePath(path);
         conn->to.flush();
         copyNAR(conn->from, sink);
     }
@@ -280,7 +280,7 @@ public:
         auto conn(connections->get());
 
         conn->to
-            << cmdBuildDerivation
+            << ServeProto::Command::BuildDerivation
             << printStorePath(drvPath);
         writeDerivation(conn->to, *this, drv);
 
@@ -311,7 +311,7 @@ public:
 
         auto conn(connections->get());
 
-        conn->to << cmdBuildPaths;
+        conn->to << ServeProto::Command::BuildPaths;
         Strings ss;
         for (auto & p : drvPaths) {
             auto sOrDrvPath = StorePathWithOutputs::tryFromDerivedPath(p);
@@ -368,7 +368,7 @@ public:
         auto conn(connections->get());
 
         conn->to
-            << cmdQueryClosure
+            << ServeProto::Command::QueryClosure
             << includeOutputs;
         WorkerProto::write(*this, conn->to, paths);
         conn->to.flush();
@@ -383,7 +383,7 @@ public:
         auto conn(connections->get());
 
         conn->to
-            << cmdQueryValidPaths
+            << ServeProto::Command::QueryValidPaths
             << false // lock
             << maybeSubstitute;
         WorkerProto::write(*this, conn->to, paths);
diff --git a/src/libstore/serve-protocol.hh b/src/libstore/serve-protocol.hh
index 553fd3a09..7e43b3969 100644
--- a/src/libstore/serve-protocol.hh
+++ b/src/libstore/serve-protocol.hh
@@ -10,16 +10,52 @@ namespace nix {
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
-typedef enum {
-    cmdQueryValidPaths = 1,
-    cmdQueryPathInfos = 2,
-    cmdDumpStorePath = 3,
-    cmdImportPaths = 4,
-    cmdExportPaths = 5,
-    cmdBuildPaths = 6,
-    cmdQueryClosure = 7,
-    cmdBuildDerivation = 8,
-    cmdAddToStoreNar = 9,
-} ServeCommand;
+/**
+ * The "serve protocol", used by ssh:// stores.
+ *
+ * This `struct` is basically just a `namespace`; We use a type rather
+ * than a namespace just so we can use it as a template argument.
+ */
+struct ServeProto
+{
+    /**
+     * Enumeration of all the request types for the protocol.
+     */
+    enum struct Command : uint64_t;
+};
+
+enum struct ServeProto::Command : uint64_t
+{
+    QueryValidPaths = 1,
+    QueryPathInfos = 2,
+    DumpStorePath = 3,
+    ImportPaths = 4,
+    ExportPaths = 5,
+    BuildPaths = 6,
+    QueryClosure = 7,
+    BuildDerivation = 8,
+    AddToStoreNar = 9,
+};
+
+/**
+ * Convenience for sending operation codes.
+ *
+ * @todo Switch to using `ServeProto::Serialize` instead probably. But
+ * this was not done at this time so there would be less churn.
+ */
+inline Sink & operator << (Sink & sink, ServeProto::Command op)
+{
+    return sink << (uint64_t) op;
+}
+
+/**
+ * Convenience for debugging.
+ *
+ * @todo Perhaps render known opcodes more nicely.
+ */
+inline std::ostream & operator << (std::ostream & s, ServeProto::Command op)
+{
+    return s << (uint64_t) op;
+}
 
 }
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 1558ac11e..062c68ff8 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -838,16 +838,16 @@ static void opServe(Strings opFlags, Strings opArgs)
     };
 
     while (true) {
-        ServeCommand cmd;
+        ServeProto::Command cmd;
         try {
-            cmd = (ServeCommand) readInt(in);
+            cmd = (ServeProto::Command) readInt(in);
         } catch (EndOfFile & e) {
             break;
         }
 
         switch (cmd) {
 
-            case cmdQueryValidPaths: {
+            case ServeProto::Command::QueryValidPaths: {
                 bool lock = readInt(in);
                 bool substitute = readInt(in);
                 auto paths = WorkerProto::Serialise<StorePathSet>::read(*store, in);
@@ -863,7 +863,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 break;
             }
 
-            case cmdQueryPathInfos: {
+            case ServeProto::Command::QueryPathInfos: {
                 auto paths = WorkerProto::Serialise<StorePathSet>::read(*store, in);
                 // !!! Maybe we want a queryPathInfos?
                 for (auto & i : paths) {
@@ -886,24 +886,24 @@ static void opServe(Strings opFlags, Strings opArgs)
                 break;
             }
 
-            case cmdDumpStorePath:
+            case ServeProto::Command::DumpStorePath:
                 store->narFromPath(store->parseStorePath(readString(in)), out);
                 break;
 
-            case cmdImportPaths: {
+            case ServeProto::Command::ImportPaths: {
                 if (!writeAllowed) throw Error("importing paths is not allowed");
                 store->importPaths(in, NoCheckSigs); // FIXME: should we skip sig checking?
                 out << 1; // indicate success
                 break;
             }
 
-            case cmdExportPaths: {
+            case ServeProto::Command::ExportPaths: {
                 readInt(in); // obsolete
                 store->exportPaths(WorkerProto::Serialise<StorePathSet>::read(*store, in), out);
                 break;
             }
 
-            case cmdBuildPaths: {
+            case ServeProto::Command::BuildPaths: {
 
                 if (!writeAllowed) throw Error("building paths is not allowed");
 
@@ -924,7 +924,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 break;
             }
 
-            case cmdBuildDerivation: { /* Used by hydra-queue-runner. */
+            case ServeProto::Command::BuildDerivation: { /* Used by hydra-queue-runner. */
 
                 if (!writeAllowed) throw Error("building paths is not allowed");
 
@@ -951,7 +951,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 break;
             }
 
-            case cmdQueryClosure: {
+            case ServeProto::Command::QueryClosure: {
                 bool includeOutputs = readInt(in);
                 StorePathSet closure;
                 store->computeFSClosure(WorkerProto::Serialise<StorePathSet>::read(*store, in),
@@ -960,7 +960,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 break;
             }
 
-            case cmdAddToStoreNar: {
+            case ServeProto::Command::AddToStoreNar: {
                 if (!writeAllowed) throw Error("importing paths is not allowed");
 
                 auto path = readString(in);