diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index d69d3a0c2..519e03242 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -137,11 +137,8 @@ static int main_build_remote(int argc, char * * argv)
                 for (auto & m : machines) {
                     debug("considering building on remote machine '%s'", m.storeUri);
 
-                    if (m.enabled
-                        && (neededSystem == "builtin"
-                            || std::find(m.systemTypes.begin(),
-                                m.systemTypes.end(),
-                                neededSystem) != m.systemTypes.end()) &&
+                    if (m.enabled &&
+                        m.systemSupported(neededSystem) &&
                         m.allSupported(requiredFeatures) &&
                         m.mandatoryMet(requiredFeatures))
                     {
@@ -214,7 +211,7 @@ static int main_build_remote(int argc, char * * argv)
 
                         for (auto & m : machines)
                             error
-                                % concatStringsSep<std::vector<std::string>>(", ", m.systemTypes)
+                                % concatStringsSep<StringSet>(", ", m.systemTypes)
                                 % m.maxJobs
                                 % concatStringsSep<StringSet>(", ", m.supportedFeatures)
                                 % concatStringsSep<StringSet>(", ", m.mandatoryFeatures);
diff --git a/src/libstore/machines.cc b/src/libstore/machines.cc
index 512115893..561d8d557 100644
--- a/src/libstore/machines.cc
+++ b/src/libstore/machines.cc
@@ -38,6 +38,11 @@ Machine::Machine(decltype(storeUri) storeUri,
     sshPublicHostKey(sshPublicHostKey)
 {}
 
+bool Machine::systemSupported(const std::string & system) const
+{
+    return system == "builtin" || (systemTypes.count(system) > 0);
+}
+
 bool Machine::allSupported(const std::set<std::string> & features) const
 {
     return std::all_of(features.begin(), features.end(),
@@ -145,7 +150,7 @@ static Machine parseBuilderLine(const std::string & line)
 
     return {
         tokens[0],
-        isSet(1) ? tokenizeString<std::vector<std::string>>(tokens[1], ",") : std::vector<std::string>{settings.thisSystem},
+        isSet(1) ? tokenizeString<std::set<std::string>>(tokens[1], ",") : std::set<std::string>{settings.thisSystem},
         isSet(2) ? tokens[2] : "",
         isSet(3) ? parseUnsignedIntField(3) : 1U,
         isSet(4) ? parseUnsignedIntField(4) : 1U,
diff --git a/src/libstore/machines.hh b/src/libstore/machines.hh
index 1adeaf1f0..1bca74c28 100644
--- a/src/libstore/machines.hh
+++ b/src/libstore/machines.hh
@@ -10,7 +10,7 @@ class Store;
 struct Machine {
 
     const std::string storeUri;
-    const std::vector<std::string> systemTypes;
+    const std::set<std::string> systemTypes;
     const std::string sshKey;
     const unsigned int maxJobs;
     const unsigned int speedFactor;
@@ -19,8 +19,21 @@ struct Machine {
     const std::string sshPublicHostKey;
     bool enabled = true;
 
+    /**
+     * @return Whether `system` is either `"builtin"` or in
+     * `systemTypes`.
+     */
+    bool systemSupported(const std::string & system) const;
+
+    /**
+     * @return Whether `features` is a subset of the union of `supportedFeatures` and
+     * `mandatoryFeatures`
+     */
     bool allSupported(const std::set<std::string> & features) const;
 
+    /**
+     * @return @Whether `mandatoryFeatures` is a subset of `features`
+     */
     bool mandatoryMet(const std::set<std::string> & features) const;
 
     Machine(decltype(storeUri) storeUri,