diff --git a/common/project.cpp b/common/project.cpp
index df7513544f..244f96b67f 100644
--- a/common/project.cpp
+++ b/common/project.cpp
@@ -33,6 +33,7 @@
 #include <string_utils.h>
 #include <kiface_ids.h>
 #include <kiway.h>
+#include <lockfile.h>
 #include <macros.h>
 #include <project.h>
 #include <project/project_file.h>
@@ -42,6 +43,7 @@
 #include <settings/settings_manager.h>
 #include <title_block.h>
 
+
 PROJECT::PROJECT() :
         m_readOnly( false ),
         m_textVarsTicker( 0 ),
@@ -460,3 +462,15 @@ DESIGN_BLOCK_LIB_TABLE* PROJECT::DesignBlockLibs()
 
     return tbl;
 }
+
+
+void PROJECT::SetProjectLock( LOCKFILE* aLockFile )
+{
+    m_project_lock.reset( aLockFile );
+}
+
+
+LOCKFILE* PROJECT::GetProjectLock() const
+{
+    return m_project_lock.get();
+}
\ No newline at end of file
diff --git a/common/settings/settings_manager.cpp b/common/settings/settings_manager.cpp
index 0198742e64..04d840a369 100644
--- a/common/settings/settings_manager.cpp
+++ b/common/settings/settings_manager.cpp
@@ -939,13 +939,11 @@ bool SETTINGS_MANAGER::LoadProject( const wxString& aFullPath, bool aSetActive )
     if( m_projects.count( fullPath ) )
         return true;
 
-    bool readOnly = false;
     LOCKFILE lockFile( fullPath );
 
     if( !lockFile.Valid() )
     {
         wxLogTrace( traceSettings, wxT( "Project %s is locked; opening read-only" ), fullPath );
-        readOnly = true;
     }
 
     // No MDI yet
@@ -986,10 +984,10 @@ bool SETTINGS_MANAGER::LoadProject( const wxString& aFullPath, bool aSetActive )
 
     if( success )
     {
-        project->SetReadOnly( readOnly || project->GetProjectFile().IsReadOnly() );
+        project->SetReadOnly( !lockFile.Valid() || project->GetProjectFile().IsReadOnly() );
 
         if( lockFile && aSetActive )
-            m_project_lock.reset( new LOCKFILE( std::move( lockFile ) ) );
+            project->SetProjectLock( new LOCKFILE( std::move( lockFile ) ) );
     }
 
     m_projects_list.push_back( std::move( project ) );
@@ -1048,9 +1046,6 @@ bool SETTINGS_MANAGER::UnloadProject( PROJECT* aProject, bool aSave )
         // Remove the reference in the environment to the previous project
         wxSetEnv( PROJECT_VAR_NAME, wxS( "" ) );
 
-        // Release lock on the file, in case we had one
-        m_project_lock = nullptr;
-
         if( m_kiway )
             m_kiway->ProjectChanged();
     }
diff --git a/include/lockfile.h b/include/lockfile.h
index 54bcbb6a59..190e59f5d0 100644
--- a/include/lockfile.h
+++ b/include/lockfile.h
@@ -127,6 +127,20 @@ public:
         }
     }
 
+    LOCKFILE( LOCKFILE&& other ) noexcept :
+            m_originalFile( std::move( other.m_originalFile ) ),
+            m_lockFilename( std::move( other.m_lockFilename ) ),
+            m_username( std::move( other.m_username ) ),
+            m_hostname( std::move( other.m_hostname ) ),
+            m_fileCreated( other.m_fileCreated ),
+            m_status( other.m_status ),
+            m_removeOnRelease( other.m_removeOnRelease ),
+            m_errorMsg( std::move( other.m_errorMsg ) )
+    {
+        // Disable unlock in the moved-from object
+        other.m_fileCreated = false;
+    }
+
     ~LOCKFILE()
     {
         UnlockFile();
diff --git a/include/project.h b/include/project.h
index a31b12c966..2e153cd92e 100644
--- a/include/project.h
+++ b/include/project.h
@@ -52,6 +52,7 @@ class SYMBOL_LIB_TABLE;
 class FILENAME_RESOLVER;
 class PROJECT_FILE;
 class PROJECT_LOCAL_SETTINGS;
+class LOCKFILE;
 
 
 /**
@@ -217,9 +218,9 @@ public:
     {
         DOC_PATH,
         SCH_LIB_PATH,
-        SCH_LIB_SELECT,               // eeschema/selpart.cpp
+        SCH_LIB_SELECT, // eeschema/selpart.cpp
         SCH_LIBEDIT_CUR_LIB,
-        SCH_LIBEDIT_CUR_SYMBOL,       // eeschema/libeditframe.cpp
+        SCH_LIBEDIT_CUR_SYMBOL, // eeschema/libeditframe.cpp
 
         VIEWER_3D_PATH,
         VIEWER_3D_FILTER_INDEX,
@@ -270,11 +271,11 @@ public:
     /**
      * Clear the _ELEMs and RSTRINGs.
      */
-    void Clear()        // inline not virtual
+    void Clear() // inline not virtual
     {
         elemsClear();
 
-        for( unsigned i = 0; i<RSTRING_COUNT;  ++i )
+        for( unsigned i = 0; i < RSTRING_COUNT; ++i )
             SetRString( RSTRING_T( i ), wxEmptyString );
     }
 
@@ -297,6 +298,10 @@ public:
      */
     virtual DESIGN_BLOCK_LIB_TABLE* DesignBlockLibs();
 
+    void SetProjectLock( LOCKFILE* aLockFile );
+
+    LOCKFILE* GetProjectLock() const;
+ 
 private:
     friend class SETTINGS_MANAGER; // so that SM can set project path
     friend class TEST_NETLISTS_FIXTURE; // TODO(JE) make this not required
@@ -366,6 +371,9 @@ private:
 
     /// @see this::Elem() and enum ELEM_T.
     std::array<_ELEM*,static_cast<unsigned int>( PROJECT::ELEM::COUNT )> m_elems;
+
+    /// Lock
+    std::unique_ptr<LOCKFILE> m_project_lock;
 };
 
 
diff --git a/include/settings/settings_manager.h b/include/settings/settings_manager.h
index 9c13d2c907..cf32ac0b76 100644
--- a/include/settings/settings_manager.h
+++ b/include/settings/settings_manager.h
@@ -531,9 +531,6 @@ private:
     /// Loaded project files, mapped according to project full name.
     std::map<wxString, PROJECT_FILE*> m_project_files;
 
-    /// Lock for loaded project (expand to multiple once we support MDI).
-    std::unique_ptr<LOCKFILE> m_project_lock;
-
     static wxString backupDateTimeFormat;
 };
 
diff --git a/kicad/kicad_manager_frame.cpp b/kicad/kicad_manager_frame.cpp
index da55f7f6ac..5550bba563 100644
--- a/kicad/kicad_manager_frame.cpp
+++ b/kicad/kicad_manager_frame.cpp
@@ -48,6 +48,7 @@
 #include <kiway.h>
 #include <kiway_express.h>
 #include <launch_ext.h>
+#include <lockfile.h>
 #include <notifications_manager.h>
 #include <reporter.h>
 #include <project/project_local_settings.h>
@@ -68,6 +69,7 @@
 #include <wx/filedlg.h>
 #include <wx/dnd.h>
 #include <wx/process.h>
+#include <wx/snglinst.h>
 #include <atomic>
 #include <update_manager.h>
 #include <jobs/jobset.h>
@@ -1035,7 +1037,42 @@ void KICAD_MANAGER_FRAME::CommonSettingsChanged( int aFlags )
 
 void KICAD_MANAGER_FRAME::ProjectChanged()
 {
-    wxString file  = GetProjectFileName();
+    wxString file = GetProjectFileName();
+
+    // empty file string means no project loaded
+    if( !Prj().IsNullProject() &&
+        Prj().GetProjectLock() == nullptr )
+    {
+        LOCKFILE lockFile( file );
+
+        if( !lockFile.Valid() && lockFile.IsLockedByMe() )
+        {
+            // If we cannot acquire the lock but we appear to be the one who
+            // locked it, check to see if there is another KiCad instance running.
+            // If there is not, then we can override the lock.  This could happen if
+            // KiCad crashed or was interrupted
+            if( !Pgm().SingleInstance()->IsAnotherRunning() )
+            {
+                lockFile.OverrideLock();
+            }
+        }
+
+        if( !lockFile.Valid() )
+        {
+            wxString msg;
+            msg.Printf( _( "Project '%s' is already open by '%s' at '%s'." ), file, lockFile.GetUsername(),
+                        lockFile.GetHostname() );
+
+            if( AskOverrideLock( this, msg ) )
+            {
+                lockFile.OverrideLock();
+            }
+        }
+
+        Prj().SetReadOnly( !lockFile.Valid() || Prj().GetProjectFile().IsReadOnly() );
+        Prj().SetProjectLock( new LOCKFILE( std::move( lockFile ) ) );
+    }
+
     wxString title;
 
     if( !file.IsEmpty() )