diff --git a/onionshare_gui/__init__.py b/onionshare_gui/__init__.py
index d083f741..c2605e81 100644
--- a/onionshare_gui/__init__.py
+++ b/onionshare_gui/__init__.py
@@ -24,6 +24,8 @@ import platform
 import argparse
 import signal
 import json
+import psutil
+import getpass
 from PyQt5 import QtCore, QtWidgets
 
 from onionshare.common import Common
@@ -125,23 +127,38 @@ def main():
         with open(common.gui.lock_filename, "r") as f:
             existing_pid = int(f.read())
 
-        print(f"Opening tab in existing OnionShare window (pid {existing_pid})")
-
-        # Make an event for the existing OnionShare window
-        if filenames:
-            obj = {"type": "new_share_tab", "filenames": filenames}
+        # Is this process actually still running?
+        still_running = True
+        if not psutil.pid_exists(existing_pid):
+            still_running = False
         else:
-            obj = {"type": "new_tab"}
+            for proc in psutil.process_iter(["pid", "name", "username"]):
+                if proc.pid == existing_pid:
+                    if (
+                        proc.username() != getpass.getuser()
+                        or "onionshare" not in " ".join(proc.cmdline()).lower()
+                    ):
+                        still_running = False
 
-        # Write that event to disk
-        with open(common.gui.events_filename, "a") as f:
-            f.write(json.dumps(obj) + "\n")
-        return
+        if still_running:
+            print(f"Opening tab in existing OnionShare window (pid {existing_pid})")
 
-    else:
-        # Write the lock file
-        with open(common.gui.lock_filename, "w") as f:
-            f.write(f"{os.getpid()}\n")
+            # Make an event for the existing OnionShare window
+            if filenames:
+                obj = {"type": "new_share_tab", "filenames": filenames}
+            else:
+                obj = {"type": "new_tab"}
+
+            # Write that event to disk
+            with open(common.gui.events_filename, "a") as f:
+                f.write(json.dumps(obj) + "\n")
+            return
+        else:
+            os.remove(common.gui.lock_filename)
+
+    # Write the lock file
+    with open(common.gui.lock_filename, "w") as f:
+        f.write(f"{os.getpid()}\n")
 
     # Allow Ctrl-C to smoothly quit the program instead of throwing an exception
     def signal_handler(s, frame):
diff --git a/poetry.lock b/poetry.lock
index 7dd361aa..a9780ff4 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -312,6 +312,17 @@ version = ">=0.12"
 [package.extras]
 dev = ["pre-commit", "tox"]
 
+[[package]]
+category = "main"
+description = "Cross-platform lib for process and system monitoring in Python."
+name = "psutil"
+optional = false
+python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
+version = "5.7.2"
+
+[package.extras]
+test = ["ipaddress", "mock", "unittest2", "enum34", "pywin32", "wmi"]
+
 [[package]]
 category = "dev"
 description = "library with cross-python path, ini-parsing, io, code, log facilities"
@@ -590,7 +601,7 @@ docs = ["sphinx", "jaraco.packaging (>=3.2)", "rst.linker (>=1.9)"]
 testing = ["jaraco.itertools", "func-timeout"]
 
 [metadata]
-content-hash = "04baf07d49586f9567f78935d759b4245d75ed42cba8bdfe0bdb6a3bc9533aee"
+content-hash = "b5a36d265c4247b98b493fac989ecdd3c11920bd4c81d47f2af9e64edb5fd5bb"
 lock-version = "1.0"
 python-versions = "^3.7"
 
@@ -755,6 +766,19 @@ pluggy = [
     {file = "pluggy-0.13.1-py2.py3-none-any.whl", hash = "sha256:966c145cd83c96502c3c3868f50408687b38434af77734af1e9ca461a4081d2d"},
     {file = "pluggy-0.13.1.tar.gz", hash = "sha256:15b2acde666561e1298d71b523007ed7364de07029219b604cf808bfa1c765b0"},
 ]
+psutil = [
+    {file = "psutil-5.7.2-cp27-none-win32.whl", hash = "sha256:f2018461733b23f308c298653c8903d32aaad7873d25e1d228765e91ae42c3f2"},
+    {file = "psutil-5.7.2-cp27-none-win_amd64.whl", hash = "sha256:66c18ca7680a31bf16ee22b1d21b6397869dda8059dbdb57d9f27efa6615f195"},
+    {file = "psutil-5.7.2-cp35-cp35m-win32.whl", hash = "sha256:5e9d0f26d4194479a13d5f4b3798260c20cecf9ac9a461e718eb59ea520a360c"},
+    {file = "psutil-5.7.2-cp35-cp35m-win_amd64.whl", hash = "sha256:4080869ed93cce662905b029a1770fe89c98787e543fa7347f075ade761b19d6"},
+    {file = "psutil-5.7.2-cp36-cp36m-win32.whl", hash = "sha256:d8a82162f23c53b8525cf5f14a355f5d1eea86fa8edde27287dd3a98399e4fdf"},
+    {file = "psutil-5.7.2-cp36-cp36m-win_amd64.whl", hash = "sha256:0ee3c36428f160d2d8fce3c583a0353e848abb7de9732c50cf3356dd49ad63f8"},
+    {file = "psutil-5.7.2-cp37-cp37m-win32.whl", hash = "sha256:ff1977ba1a5f71f89166d5145c3da1cea89a0fdb044075a12c720ee9123ec818"},
+    {file = "psutil-5.7.2-cp37-cp37m-win_amd64.whl", hash = "sha256:a5b120bb3c0c71dfe27551f9da2f3209a8257a178ed6c628a819037a8df487f1"},
+    {file = "psutil-5.7.2-cp38-cp38-win32.whl", hash = "sha256:10512b46c95b02842c225f58fa00385c08fa00c68bac7da2d9a58ebe2c517498"},
+    {file = "psutil-5.7.2-cp38-cp38-win_amd64.whl", hash = "sha256:68d36986ded5dac7c2dcd42f2682af1db80d4bce3faa126a6145c1637e1b559f"},
+    {file = "psutil-5.7.2.tar.gz", hash = "sha256:90990af1c3c67195c44c9a889184f84f5b2320dce3ee3acbd054e3ba0b4a7beb"},
+]
 py = [
     {file = "py-1.9.0-py2.py3-none-any.whl", hash = "sha256:366389d1db726cd2fcfc79732e75410e5fe4d31db13692115529d34069a043c2"},
     {file = "py-1.9.0.tar.gz", hash = "sha256:9ca6883ce56b4e8da7e79ac18787889fa5206c79dcc67fb065376cd2fe03f342"},
diff --git a/pyproject.toml b/pyproject.toml
index 171f7c47..6011b976 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -31,6 +31,7 @@ Werkzeug = "*"
 flask-socketio = "^4.3.0"
 eventlet = "^0.25.2"
 qrcode = "^6.1"
+psutil = "^5.7.2"
 
 [tool.poetry.dev-dependencies]
 atomicwrites = "*"