diff --git a/proton b/proton
index a781e396..51c3041e 100755
--- a/proton
+++ b/proton
@@ -113,140 +113,142 @@ with dist_lock:
 prefix = os.environ["STEAM_COMPAT_DATA_PATH"] + "/pfx/"
 env["WINEPREFIX"] = prefix
 
-if not os.path.isdir(prefix):
-    #copy default prefix into place
-    shutil.copytree(basedir + "/dist/share/default_pfx", prefix, symlinks=True)
+prefix_lock = FileLock(os.environ["STEAM_COMPAT_DATA_PATH"] + "/pfx.lock", timeout=-1)
+with prefix_lock:
+    if not os.path.isdir(prefix):
+        #copy default prefix into place
+        shutil.copytree(basedir + "/dist/share/default_pfx", prefix, symlinks=True)
 
-version_file = os.environ["STEAM_COMPAT_DATA_PATH"] + "/version"
-if os.path.exists(version_file):
-    with open(version_file, "r") as f:
-        upgrade_pfx(f.readline().strip())
-else:
-    upgrade_pfx(None)
+    version_file = os.environ["STEAM_COMPAT_DATA_PATH"] + "/version"
+    if os.path.exists(version_file):
+        with open(version_file, "r") as f:
+            upgrade_pfx(f.readline().strip())
+    else:
+        upgrade_pfx(None)
 
-with open(version_file, "w") as f:
-    f.write(CURRENT_PREFIX_VERSION + "\n")
+    with open(version_file, "w") as f:
+        f.write(CURRENT_PREFIX_VERSION + "\n")
 
-#copy steam files into place
-if "STEAM_COMPAT_CLIENT_INSTALL_PATH" in os.environ:
-    #modern steam client sets this
-    steamdir = os.environ["STEAM_COMPAT_CLIENT_INSTALL_PATH"]
-elif "STEAM_CLIENT_CONFIG_FILE" in os.environ:
-    #fallback for old steam clients (should remove once changes graduate)
-    steamdir = os.path.dirname(os.environ["STEAM_CLIENT_CONFIG_FILE"])
-else:
-    #linux-only fallback, really shouldn't get here
-    steamdir = os.environ["HOME"] + ".steam/root/"
-dst = prefix + "/drive_c/Program Files (x86)/"
-makedirs(dst + "Steam")
-filestocopy = ["steamclient.dll",
-        "steamclient64.dll",
-        "Steam.dll"]
-for f in filestocopy:
-    if os.path.isfile(steamdir + "/legacycompat/" + f):
-        dstfile = dst + "Steam/" + f
-        if os.path.isfile(dstfile):
-            os.remove(dstfile)
-        shutil.copy(steamdir + "/legacycompat/" + f, dstfile)
+    #copy steam files into place
+    if "STEAM_COMPAT_CLIENT_INSTALL_PATH" in os.environ:
+        #modern steam client sets this
+        steamdir = os.environ["STEAM_COMPAT_CLIENT_INSTALL_PATH"]
+    elif "STEAM_CLIENT_CONFIG_FILE" in os.environ:
+        #fallback for old steam clients (should remove once changes graduate)
+        steamdir = os.path.dirname(os.environ["STEAM_CLIENT_CONFIG_FILE"])
+    else:
+        #linux-only fallback, really shouldn't get here
+        steamdir = os.environ["HOME"] + ".steam/root/"
+    dst = prefix + "/drive_c/Program Files (x86)/"
+    makedirs(dst + "Steam")
+    filestocopy = ["steamclient.dll",
+            "steamclient64.dll",
+            "Steam.dll"]
+    for f in filestocopy:
+        if os.path.isfile(steamdir + "/legacycompat/" + f):
+            dstfile = dst + "Steam/" + f
+            if os.path.isfile(dstfile):
+                os.remove(dstfile)
+            shutil.copy(steamdir + "/legacycompat/" + f, dstfile)
 
-#copy openvr files into place
-dst = prefix + "/drive_c/vrclient/bin/"
-makedirs(dst)
-shutil.copy(basedir + "/dist/lib/wine/fakedlls/vrclient.dll", dst)
-shutil.copy(basedir + "/dist/lib64/wine/fakedlls/vrclient_x64.dll", dst)
+    #copy openvr files into place
+    dst = prefix + "/drive_c/vrclient/bin/"
+    makedirs(dst)
+    shutil.copy(basedir + "/dist/lib/wine/fakedlls/vrclient.dll", dst)
+    shutil.copy(basedir + "/dist/lib64/wine/fakedlls/vrclient_x64.dll", dst)
 
-#parse linux openvr config and present it in win32 format to the app.
-#logic from openvr's CVRPathRegistry_Public::GetPaths
+    #parse linux openvr config and present it in win32 format to the app.
+    #logic from openvr's CVRPathRegistry_Public::GetPaths
 
-#check environment for overrides
-vr_runtime = None
-if "VR_OVERRIDE" in env:
-    vr_runtime = env["VR_OVERRIDE"]
-    env.pop("VR_OVERRIDE")
+    #check environment for overrides
+    vr_runtime = None
+    if "VR_OVERRIDE" in env:
+        vr_runtime = env["VR_OVERRIDE"]
+        env.pop("VR_OVERRIDE")
 
-vr_config = None
-if "VR_CONFIG_PATH" in env:
-    vr_config = env["VR_CONFIG_PATH"]
-    env.pop("VR_CONFIG_PATH")
+    vr_config = None
+    if "VR_CONFIG_PATH" in env:
+        vr_config = env["VR_CONFIG_PATH"]
+        env.pop("VR_CONFIG_PATH")
 
-vr_log = None
-if "VR_LOG_PATH" in env:
-    vr_log = env["VR_LOG_PATH"]
-    env.pop("VR_LOG_PATH")
+    vr_log = None
+    if "VR_LOG_PATH" in env:
+        vr_log = env["VR_LOG_PATH"]
+        env.pop("VR_LOG_PATH")
 
-#load from json if needed
-if vr_runtime is None or \
-        vr_config is None or \
-        vr_log is None:
-    try:
-        #TODO: support mac
-        if "XDG_CONFIG_HOME" in os.environ:
-            path = os.environ["XDG_CONFIG_HOME"]
-        else:
-            path = os.environ["HOME"] + "/.config"
-        path = path + "/openvr/openvrpaths.vrpath"
+    #load from json if needed
+    if vr_runtime is None or \
+            vr_config is None or \
+            vr_log is None:
+        try:
+            #TODO: support mac
+            if "XDG_CONFIG_HOME" in os.environ:
+                path = os.environ["XDG_CONFIG_HOME"]
+            else:
+                path = os.environ["HOME"] + "/.config"
+            path = path + "/openvr/openvrpaths.vrpath"
 
-        j = json.load(open(path, "r"))
+            j = json.load(open(path, "r"))
 
-        if vr_runtime is None:
-            vr_runtime = j["runtime"][0]
+            if vr_runtime is None:
+                vr_runtime = j["runtime"][0]
 
-        if vr_config is None:
-            vr_config = j["config"][0]
+            if vr_config is None:
+                vr_config = j["config"][0]
 
-        if vr_log is None:
-            vr_log = j["log"][0]
-    except:
-        pass
+            if vr_log is None:
+                vr_log = j["log"][0]
+        except:
+            pass
 
-makedirs(prefix + "/drive_c/users/steamuser/Local Settings/Application Data/openvr")
+    makedirs(prefix + "/drive_c/users/steamuser/Local Settings/Application Data/openvr")
 
-#remove existing file
-vrpaths_name = prefix + "/drive_c/users/steamuser/Local Settings/Application Data/openvr/openvrpaths.vrpath"
-if os.path.exists(vrpaths_name):
-    os.remove(vrpaths_name)
+    #remove existing file
+    vrpaths_name = prefix + "/drive_c/users/steamuser/Local Settings/Application Data/openvr/openvrpaths.vrpath"
+    if os.path.exists(vrpaths_name):
+        os.remove(vrpaths_name)
 
-#dump new file
-if not vr_runtime is None:
-    try:
-        env["PROTON_VR_RUNTIME"] = vr_runtime
+    #dump new file
+    if not vr_runtime is None:
+        try:
+            env["PROTON_VR_RUNTIME"] = vr_runtime
 
-        j = { "runtime": [ "C:\\vrclient\\", "C:\\vrclient" ] }
+            j = { "runtime": [ "C:\\vrclient\\", "C:\\vrclient" ] }
 
-        if not vr_config is None:
-            win_vr_config = subprocess.check_output([wine_path, "winepath", "-w", vr_config], env=env, stderr=lfile)
-            j["config"] = [ win_vr_config.strip() ]
+            if not vr_config is None:
+                win_vr_config = subprocess.check_output([wine_path, "winepath", "-w", vr_config], env=env, stderr=lfile)
+                j["config"] = [ win_vr_config.strip() ]
 
-        if not vr_log is None:
-            win_vr_log = subprocess.check_output([wine_path, "winepath", "-w", vr_log], env=env, stderr=lfile)
-            j["log"] = [ win_vr_log.strip() ]
+            if not vr_log is None:
+                win_vr_log = subprocess.check_output([wine_path, "winepath", "-w", vr_log], env=env, stderr=lfile)
+                j["log"] = [ win_vr_log.strip() ]
 
-        j["version"] = 1
-        j["jsonid"] = "vrpathreg"
+            j["version"] = 1
+            j["jsonid"] = "vrpathreg"
 
-        json.dump(j, open(vrpaths_name, "w"), indent=2)
-    except:
-        pass
+            json.dump(j, open(vrpaths_name, "w"), indent=2)
+        except:
+            pass
 
-def make_dxvk_links(dll_dir, link_dir):
-    if os.path.lexists(link_dir + "/d3d11.dll"):
-        os.remove(link_dir + "/d3d11.dll")
-    if os.path.lexists(link_dir + "/dxgi.dll"):
-        os.remove(link_dir + "/dxgi.dll")
-    os.symlink(dll_dir + "/d3d11.dll", link_dir + "/d3d11.dll")
-    os.symlink(dll_dir + "/dxgi.dll", link_dir + "/dxgi.dll")
+    def make_dxvk_links(dll_dir, link_dir):
+        if os.path.lexists(link_dir + "/d3d11.dll"):
+            os.remove(link_dir + "/d3d11.dll")
+        if os.path.lexists(link_dir + "/dxgi.dll"):
+            os.remove(link_dir + "/dxgi.dll")
+        os.symlink(dll_dir + "/d3d11.dll", link_dir + "/d3d11.dll")
+        os.symlink(dll_dir + "/dxgi.dll", link_dir + "/dxgi.dll")
 
-if "dxvk" in config_opts:
-    make_dxvk_links(basedir + "/dist/lib64/wine/dxvk/",
-        prefix + "drive_c/windows/system32")
-    make_dxvk_links(basedir + "/dist/lib/wine/dxvk/",
-        prefix + "drive_c/windows/syswow64")
-    env["WINEDLLOVERRIDES"] = "dxgi,d3d11=n"
-else:
-    make_dxvk_links(basedir + "/dist/lib64/wine/",
-        prefix + "drive_c/windows/system32")
-    make_dxvk_links(basedir + "/dist/lib/wine/",
-        prefix + "drive_c/windows/syswow64")
+    if "dxvk" in config_opts:
+        make_dxvk_links(basedir + "/dist/lib64/wine/dxvk/",
+            prefix + "drive_c/windows/system32")
+        make_dxvk_links(basedir + "/dist/lib/wine/dxvk/",
+            prefix + "drive_c/windows/syswow64")
+        env["WINEDLLOVERRIDES"] = "dxgi,d3d11=n"
+    else:
+        make_dxvk_links(basedir + "/dist/lib64/wine/",
+            prefix + "drive_c/windows/system32")
+        make_dxvk_links(basedir + "/dist/lib/wine/",
+            prefix + "drive_c/windows/syswow64")
 
 ARCH_UNKNOWN=0
 ARCH_I386=1