diff --git a/CMakeLists.txt b/CMakeLists.txt
index d40960a..bb48e9e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -35,6 +35,7 @@ add_executable(FlashMQ
     unscopedlock.cpp
     scopedsocket.cpp
     bindaddr.cpp
+    oneinstancelock.cpp
     )
 
 target_link_libraries(FlashMQ pthread dl ssl crypto)
diff --git a/mainapp.cpp b/mainapp.cpp
index 3132cf6..c659b44 100644
--- a/mainapp.cpp
+++ b/mainapp.cpp
@@ -378,6 +378,13 @@ MainApp *MainApp::getMainApp()
 
 void MainApp::start()
 {
+#ifndef NDEBUG
+    if (fuzzFilePath.empty())
+    {
+        oneInstanceLock.lock();
+    }
+#endif
+
     timer.start();
 
     std::map<int, std::shared_ptr<Listener>> listenerMap; // For finding listeners by fd.
@@ -516,6 +523,8 @@ void MainApp::start()
         }
     }
 
+    oneInstanceLock.unlock();
+
     for(std::shared_ptr<ThreadData> &thread : threads)
     {
         thread->queueQuit();
diff --git a/mainapp.h b/mainapp.h
index 0c44522..ae64046 100644
--- a/mainapp.h
+++ b/mainapp.h
@@ -23,6 +23,7 @@
 #include "configfileparser.h"
 #include "timer.h"
 #include "scopedsocket.h"
+#include "oneinstancelock.h"
 
 class MainApp
 {
@@ -44,6 +45,7 @@ class MainApp
     std::mutex quitMutex;
     std::string fuzzFilePath;
     bool fuzzWebsockets = false;
+    OneInstanceLock oneInstanceLock;
 
     Logger *logger = Logger::getInstance();
 
diff --git a/oneinstancelock.cpp b/oneinstancelock.cpp
new file mode 100644
index 0000000..c8e39a7
--- /dev/null
+++ b/oneinstancelock.cpp
@@ -0,0 +1,56 @@
+#include "oneinstancelock.h"
+
+#include <stdexcept>
+
+#include "utils.h"
+
+OneInstanceLock::OneInstanceLock()
+{
+    std::string dir("/tmp");
+
+    char *d = getenv("HOME");
+    if (d != NULL && d[0] == '/')
+    {
+        dir = std::string(d);
+    }
+    lockFilePath = dir + "/.FlashMQ.lock";
+}
+
+OneInstanceLock::~OneInstanceLock()
+{
+    unlock();
+}
+
+void OneInstanceLock::lock()
+{
+    fd = open(lockFilePath.c_str(), O_RDWR | O_CREAT, 0600);
+    if (fd < 0)
+         throw std::runtime_error(formatString("Can't create '%s': %s", lockFilePath.c_str(), strerror(errno)));
+
+    struct flock fl;
+    fl.l_start = 0;
+    fl.l_len = 0;
+    fl.l_type = F_WRLCK;
+    fl.l_whence = SEEK_SET;
+    if (fcntl(fd, F_SETLK, &fl) < 0)
+    {
+        throw std::runtime_error("Can't acquire lock: another instance is already running?");
+    }
+}
+
+void OneInstanceLock::unlock()
+{
+    if (fd > 0)
+    {
+        close(fd);
+        fd = 0;
+        if (!lockFilePath.empty())
+        {
+            if (unlink(lockFilePath.c_str()) < 0)
+            {
+                logger->logf(LOG_ERR, "Can't delete '%': %s", lockFilePath.c_str(), strerror(errno));
+            }
+            lockFilePath.clear();
+        }
+    }
+}
diff --git a/oneinstancelock.h b/oneinstancelock.h
new file mode 100644
index 0000000..f019094
--- /dev/null
+++ b/oneinstancelock.h
@@ -0,0 +1,23 @@
+#ifndef ONEINSTANCELOCK_H
+#define ONEINSTANCELOCK_H
+
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <string>
+#include "logger.h"
+
+class OneInstanceLock
+{
+    int fd = -1;
+    std::string lockFilePath;
+    Logger *logger = Logger::getInstance();
+
+public:
+    OneInstanceLock();
+    ~OneInstanceLock();
+    void lock();
+    void unlock();
+};
+
+#endif // ONEINSTANCELOCK_H