diff --git a/src/disk_tool.h b/src/disk_tool.h
index 9e7a43c4..477aed3c 100644
--- a/src/disk_tool.h
+++ b/src/disk_tool.h
@@ -132,7 +132,6 @@ void disk_tool_simple_offsets(json11::Json cfg, bool json_output);
 
 uint64_t sscanf_json(const char *fmt, const json11::Json & str);
 void fromhexstr(const std::string & from, int bytes, uint8_t *to);
-std::string realpath_str(std::string path, bool nofail = true);
 int disable_cache(std::string dev);
 std::string get_parent_device(std::string dev);
 bool json_is_true(const json11::Json & val);
diff --git a/src/disk_tool_utils.cpp b/src/disk_tool_utils.cpp
index 8dfcfed0..ab94db85 100644
--- a/src/disk_tool_utils.cpp
+++ b/src/disk_tool_utils.cpp
@@ -42,19 +42,6 @@ void fromhexstr(const std::string & from, int bytes, uint8_t *to)
     }
 }
 
-std::string realpath_str(std::string path, bool nofail)
-{
-    char *p = realpath((char*)path.c_str(), NULL);
-    if (!p)
-    {
-        fprintf(stderr, "Failed to resolve %s: %s\n", path.c_str(), strerror(errno));
-        return nofail ? path : "";
-    }
-    std::string rp(p);
-    free(p);
-    return rp;
-}
-
 // returns 1 = check error, 0 = write through, -1 = write back
 // (similar to 1 = warning, -1 = error, 0 = success in disable_cache)
 static int check_queue_cache(std::string dev, std::string parent_dev)
diff --git a/src/nfs_proxy.cpp b/src/nfs_proxy.cpp
index 07d4e903..15060840 100644
--- a/src/nfs_proxy.cpp
+++ b/src/nfs_proxy.cpp
@@ -1032,6 +1032,7 @@ void single_child_handler(int signal)
 
 void nfs_proxy_t::mount_fs()
 {
+    check_already_mounted();
     signal(SIGCHLD, single_child_handler);
     auto pid = fork();
     if (pid < 0)
@@ -1072,6 +1073,30 @@ void nfs_proxy_t::mount_fs()
     }
 }
 
+void nfs_proxy_t::check_already_mounted()
+{
+    std::string realpoint = realpath_str(mountpoint, false);
+    if (realpoint == "")
+    {
+        return;
+    }
+    std::string mountstr = read_file("/proc/mounts");
+    if (mountstr == "")
+    {
+        return;
+    }
+    auto mounts = explode("\n", mountstr, true);
+    for (auto & str: mounts)
+    {
+        auto mnt = explode(" ", str, true);
+        if (mnt.size() >= 2 && mnt[1] == realpoint)
+        {
+            fprintf(stderr, "%s is already mounted\n", mountpoint.c_str());
+            exit(1);
+        }
+    }
+}
+
 void nfs_proxy_t::check_exit()
 {
     if (active_connections || !exit_on_umount)
@@ -1084,7 +1109,7 @@ void nfs_proxy_t::check_exit()
         return;
     }
     auto port_opt = "port="+std::to_string(listening_port);
-    auto mountport_opt = "port="+std::to_string(listening_port);
+    auto mountport_opt = "mountport="+std::to_string(listening_port);
     auto mounts = explode("\n", mountstr, true);
     for (auto & str: mounts)
     {
diff --git a/src/nfs_proxy.h b/src/nfs_proxy.h
index ae40c4d3..8dbd164e 100644
--- a/src/nfs_proxy.h
+++ b/src/nfs_proxy.h
@@ -66,6 +66,7 @@ public:
     void daemonize();
     void write_pid();
     void mount_fs();
+    void check_already_mounted();
     void check_exit();
 };
 
diff --git a/src/str_util.cpp b/src/str_util.cpp
index d96b9303..1b78f1ad 100644
--- a/src/str_util.cpp
+++ b/src/str_util.cpp
@@ -428,3 +428,16 @@ std::string auto_addslashes(const std::string & str)
     }
     return res+"\"";
 }
+
+std::string realpath_str(std::string path, bool nofail)
+{
+    char *p = realpath((char*)path.c_str(), NULL);
+    if (!p)
+    {
+        fprintf(stderr, "Failed to resolve %s: %s\n", path.c_str(), strerror(errno));
+        return nofail ? path : "";
+    }
+    std::string rp(p);
+    free(p);
+    return rp;
+}
diff --git a/src/str_util.h b/src/str_util.h
index 9c1bd8ed..3fb03be1 100644
--- a/src/str_util.h
+++ b/src/str_util.h
@@ -25,3 +25,4 @@ size_t utf8_length(const char *s);
 std::vector<std::string> explode(const std::string & sep, const std::string & value, bool trim);
 std::string scan_escaped(const std::string & cmd, size_t & pos);
 std::string auto_addslashes(const std::string & str);
+std::string realpath_str(std::string path, bool nofail = true);