diff --git a/AltStoreCore/Model/DatabaseManager.swift b/AltStoreCore/Model/DatabaseManager.swift
index 9d517039..b91a7e8e 100644
--- a/AltStoreCore/Model/DatabaseManager.swift
+++ b/AltStoreCore/Model/DatabaseManager.swift
@@ -11,6 +11,15 @@ import CoreData
 import AltSign
 import Roxas
 
+extension CFNotificationName
+{
+    fileprivate static let willAccessDatabase = CFNotificationName("com.rileytestut.AltStore.WillAccessDatabase" as CFString)
+}
+
+private let ReceivedWillAccessDatabaseNotification: @convention(c) (CFNotificationCenter?, UnsafeMutableRawPointer?, CFNotificationName?, UnsafeRawPointer?, CFDictionary?) -> Void = { (center, observer, name, object, userInfo) in
+    DatabaseManager.shared.receivedWillAccessDatabaseNotification()
+}
+
 fileprivate class PersistentContainer: RSTPersistentContainer
 {
     override class func defaultDirectoryURL() -> URL
@@ -43,10 +52,15 @@ public class DatabaseManager
     private let coordinator = NSFileCoordinator()
     private let coordinatorQueue = OperationQueue()
     
+    private var ignoreWillAccessDatabaseNotification = false
+    
     private init()
     {
         self.persistentContainer = PersistentContainer(name: "AltStore", bundle: Bundle(for: DatabaseManager.self))
         self.persistentContainer.preferredMergePolicy = MergePolicy()
+        
+        let observer = Unmanaged.passUnretained(self).toOpaque()
+        CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), observer, ReceivedWillAccessDatabaseNotification, CFNotificationName.willAccessDatabase.rawValue, nil, .deliverImmediately)
     }
 }
 
@@ -73,6 +87,10 @@ public extension DatabaseManager
             
             guard !self.isStarted else { return finish(nil) }
             
+            // Quit any other running AltStore processes to prevent concurrent database access during and after migration.
+            self.ignoreWillAccessDatabaseNotification = true
+            CFNotificationCenterPostNotification(CFNotificationCenterGetDarwinNotifyCenter(), .willAccessDatabase, nil, nil, true)
+            
             self.migrateDatabaseToAppGroupIfNeeded { (result) in
                 switch result
                 {
@@ -398,4 +416,14 @@ private extension DatabaseManager
             }
         }
     }
+    
+    func receivedWillAccessDatabaseNotification()
+    {
+        defer { self.ignoreWillAccessDatabaseNotification = false }
+        
+        // Ignore notifications sent by the current process.
+        guard !self.ignoreWillAccessDatabaseNotification else { return }
+        
+        exit(104)
+    }
 }