diff --git a/proton b/proton
index 66aa3646..5246f7e8 100755
--- a/proton
+++ b/proton
@@ -694,7 +694,7 @@ class Session:
         except (OSError, IOError, TypeError, KeyError):
             pass
 
-    def init_session(self):
+    def init_session(self, update_prefix_files):
         self.env["WINEPREFIX"] = g_compatdata.prefix_dir
 
         #load environment overrides
@@ -812,7 +812,8 @@ class Session:
         else:
             self.env["WINEDEBUG"] = "-all"
 
-        g_compatdata.setup_prefix()
+        if update_prefix_files:
+            g_compatdata.setup_prefix()
 
         if "nod3d11" in self.compat_config:
             self.dlloverrides["d3d11"] = ""
@@ -983,7 +984,7 @@ if __name__ == "__main__":
     if g_proton.missing_default_prefix():
         g_proton.make_default_prefix()
 
-    g_session.init_session()
+    g_session.init_session(sys.argv[1] != "runinprefix")
 
     #determine mode
     if sys.argv[1] == "run":
@@ -994,6 +995,8 @@ if __name__ == "__main__":
         g_session.run_proc([g_proton.wineserver_bin, "-w"])
         #then run
         g_session.run()
+    elif sys.argv[1] == "runinprefix":
+        g_session.run_proc([g_proton.wine_bin] + sys.argv[2:])
     elif sys.argv[1] == "getcompatpath":
         #linux -> windows path
         path = subprocess.check_output([g_proton.wine_bin, "winepath", "-w", sys.argv[2]], env=g_session.env, stderr=g_session.log_file)