diff --git a/src/libstore/ssh.cc b/src/libstore/ssh.cc
index 6f6deda51..fae99d75b 100644
--- a/src/libstore/ssh.cc
+++ b/src/libstore/ssh.cc
@@ -41,6 +41,11 @@ void SSHMaster::addCommonSSHOpts(Strings & args)
     args.push_back("-oLocalCommand=echo started");
 }
 
+bool SSHMaster::isMasterRunning() {
+    auto res = runProgram(RunOptions {.program = "ssh", .args = {"-O", "check", host}, .mergeStderrToStdout = true});
+    return res.first == 0;
+}
+
 std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string & command)
 {
     Path socketPath = startMaster();
@@ -97,7 +102,7 @@ std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string
 
     // Wait for the SSH connection to be established,
     // So that we don't overwrite the password prompt with our progress bar.
-    if (!fakeSSH && !useMaster) {
+    if (!fakeSSH && !useMaster && !isMasterRunning()) {
         std::string reply;
         try {
             reply = readLine(out.readSide.get());
@@ -133,6 +138,8 @@ Path SSHMaster::startMaster()
     logger->pause();
     Finally cleanup = [&]() { logger->resume(); };
 
+    bool wasMasterRunning = isMasterRunning();
+
     state->sshMaster = startProcess([&]() {
         restoreProcessContext();
 
@@ -152,13 +159,15 @@ Path SSHMaster::startMaster()
 
     out.writeSide = -1;
 
-    std::string reply;
-    try {
-        reply = readLine(out.readSide.get());
-    } catch (EndOfFile & e) { }
+    if (!wasMasterRunning) {
+        std::string reply;
+        try {
+            reply = readLine(out.readSide.get());
+        } catch (EndOfFile & e) { }
 
-    if (reply != "started")
-        throw Error("failed to start SSH master connection to '%s'", host);
+        if (reply != "started")
+            throw Error("failed to start SSH master connection to '%s'", host);
+    }
 
     return state->socketPath;
 }
diff --git a/src/libstore/ssh.hh b/src/libstore/ssh.hh
index c86a8a986..94b952af9 100644
--- a/src/libstore/ssh.hh
+++ b/src/libstore/ssh.hh
@@ -28,6 +28,7 @@ private:
     Sync<State> state_;
 
     void addCommonSSHOpts(Strings & args);
+    bool isMasterRunning();
 
 public:
 
diff --git a/tests/nixos/nix-copy.nix b/tests/nixos/nix-copy.nix
index ee8b77100..16c477bf9 100644
--- a/tests/nixos/nix-copy.nix
+++ b/tests/nixos/nix-copy.nix
@@ -23,6 +23,12 @@ in {
           nix.settings.substituters = lib.mkForce [ ];
           nix.settings.experimental-features = [ "nix-command" ];
           services.getty.autologinUser = "root";
+          programs.ssh.extraConfig = ''
+            Host *
+                ControlMaster auto
+                ControlPath ~/.ssh/master-%h:%r@%n:%p
+                ControlPersist 15m
+          '';
         };
 
       server =
@@ -62,6 +68,10 @@ in {
     client.wait_for_text("done")
     server.succeed("nix-store --check-validity ${pkgA}")
 
+    # Check that ControlMaster is working
+    client.send_chars("nix copy --to ssh://server ${pkgA} >&2; echo done\n")
+    client.wait_for_text("done")
+
     client.copy_from_host("key", "/root/.ssh/id_ed25519")
     client.succeed("chmod 600 /root/.ssh/id_ed25519")