diff --git a/src/octoprint/server/api/__init__.py b/src/octoprint/server/api/__init__.py
index 82d5d0f4..47215573 100644
--- a/src/octoprint/server/api/__init__.py
+++ b/src/octoprint/server/api/__init__.py
@@ -109,7 +109,7 @@ def firstRunSetup():
 					"pass2" in request.values.keys() and request.values["pass1"] == request.values["pass2"]:
 		# configure access control
 		s().setBoolean(["accessControl", "enabled"], True)
-		octoprint.server.userManager.addUser(request.values["user"], request.values["pass1"], True, ["user", "admin"])
+		octoprint.server.userManager.addUser(request.values["user"], request.values["pass1"], True, ["user", "admin"], overwrite=True)
 		s().setBoolean(["server", "firstRun"], False)
 	elif "ac" in request.values.keys() and not request.values["ac"] in valid_boolean_trues:
 		# disable access control
diff --git a/src/octoprint/users.py b/src/octoprint/users.py
index 1aaf2071..0a1ae128 100644
--- a/src/octoprint/users.py
+++ b/src/octoprint/users.py
@@ -106,7 +106,7 @@ class UserManager(object):
 				# old hash doesn't match either, wrong password
 				return False
 
-	def addUser(self, username, password, active, roles):
+	def addUser(self, username, password, active, roles, overwrite=False):
 		pass
 
 	def changeUserActivation(self, username, active):
@@ -214,11 +214,11 @@ class FilebasedUserManager(UserManager):
 			self._dirty = False
 		self._load()
 
-	def addUser(self, username, password, active=False, roles=None, apikey=None):
+	def addUser(self, username, password, active=False, roles=None, apikey=None, overwrite=False):
 		if not roles:
 			roles = ["user"]
 
-		if username in self._users.keys():
+		if username in self._users.keys() and not overwrite:
 			raise UserAlreadyExists(username)
 
 		self._users[username] = User(username, UserManager.createPasswordHash(password), active, roles, apikey=apikey)