diff --git a/SourceGen/DisasmProject.cs b/SourceGen/DisasmProject.cs
index d2ddcba..7943c08 100644
--- a/SourceGen/DisasmProject.cs
+++ b/SourceGen/DisasmProject.cs
@@ -120,6 +120,11 @@ namespace SourceGen {
         /// </summary>
         public CpuDef CpuDef { get; private set; }
 
+        /// <summary>
+        /// If set, changes are ignored.
+        /// </summary>
+        public bool IsReadOnly { get; set; }
+
         /// <summary>
         /// If true, plugins will execute in the main application's AppDomain instead of
         /// the sandbox.  Must be set before calling Initialize().
@@ -1785,6 +1790,9 @@ namespace SourceGen {
         /// </summary>
         /// <param name="changeSet">Set to push.</param>
         public void PushChangeSet(ChangeSet changeSet) {
+            if (IsReadOnly) {
+                return;
+            }
             Debug.WriteLine("PushChangeSet: adding " + changeSet);
 
             // Remove all of the "redo" entries from the current position to the end.
@@ -1850,6 +1858,9 @@ namespace SourceGen {
         public UndoableChange.ReanalysisScope ApplyChanges(ChangeSet cs, bool backward,
                 out RangeSet affectedOffsets) {
             affectedOffsets = new RangeSet();
+            if (IsReadOnly) {
+                return UndoableChange.ReanalysisScope.None;
+            }
 
             UndoableChange.ReanalysisScope needReanalysis = UndoableChange.ReanalysisScope.None;
 
diff --git a/SourceGen/MainController.cs b/SourceGen/MainController.cs
index 55729c8..b81f4e5 100644
--- a/SourceGen/MainController.cs
+++ b/SourceGen/MainController.cs
@@ -626,9 +626,7 @@ namespace SourceGen {
         private void UpdateTitle() {
             // Update main window title.
             StringBuilder sb = new StringBuilder();
-            sb.Append(Res.Strings.TITLE_BASE);
             if (mProject != null) {
-                sb.Append(" - ");
                 if (string.IsNullOrEmpty(mProjectPathName)) {
                     sb.Append(Res.Strings.TITLE_NEW_PROJECT);
                 } else {
@@ -639,7 +637,14 @@ namespace SourceGen {
                     sb.Append(" ");
                     sb.Append(Res.Strings.TITLE_MODIFIED);
                 }
+
+                if (mProject.IsReadOnly) {
+                    sb.Append(" ");
+                    sb.Append(Res.Strings.TITLE_READ_ONLY);
+                }
+                sb.Append(" - ");
             }
+            sb.Append(Res.Strings.TITLE_BASE);
             mMainWin.Title = sb.ToString();
         }
 
@@ -1082,6 +1087,8 @@ namespace SourceGen {
                 if (ok != true) {
                     return;
                 }
+
+                newProject.IsReadOnly = dlg.WantReadOnly;
             }
 
             mProject = newProject;
@@ -1175,6 +1182,7 @@ namespace SourceGen {
         /// </summary>
         /// <returns>True on success, false if the save attempt failed or was canceled.</returns>
         public bool SaveProjectAs() {
+            Debug.Assert(!mProject.IsReadOnly);
             SaveFileDialog fileDlg = new SaveFileDialog() {
                 Filter = ProjectFile.FILENAME_FILTER + "|" + Res.Strings.FILE_FILTER_ALL,
                 FilterIndex = 1,
@@ -1205,6 +1213,7 @@ namespace SourceGen {
         /// </summary>
         /// <returns>True on success, false if the save attempt failed.</returns>
         public bool SaveProject() {
+            Debug.Assert(!mProject.IsReadOnly);
             if (string.IsNullOrEmpty(mProjectPathName)) {
                 return SaveProjectAs();
             }
@@ -1317,8 +1326,11 @@ namespace SourceGen {
             return true;
         }
 
-        public bool IsProjectOpen() {
-            return mProject != null;
+        public bool IsProjectOpen {
+            get { return mProject != null; }
+        }
+        public bool IsProjectReadOnly {
+            get { return mProject != null && mProject.IsReadOnly; }
         }
 
         public void AssembleProject() {
diff --git a/SourceGen/Res/Strings.xaml b/SourceGen/Res/Strings.xaml
index e405957..759a5b3 100644
--- a/SourceGen/Res/Strings.xaml
+++ b/SourceGen/Res/Strings.xaml
@@ -53,7 +53,7 @@ limitations under the License.
     <system:String x:Key="str_ErrBadSymbolSt">Unknown Source or Type in symbol</system:String>
     <system:String x:Key="str_ErrBadSymrefPart">Bad symbol reference part</system:String>
     <system:String x:Key="str_ErrBadTypeHint">Type hint not recognized</system:String>
-    <system:String x:Key="str_ErrDuplicateLabelFmt">Removing duplicate label '{0}' (offset +{1:x6})</system:String>
+    <system:String x:Key="str_ErrDuplicateLabelFmt">Removed duplicate label '{0}' (offset +{1:x6})</system:String>
     <system:String x:Key="str_ErrFileCopyFailedFmt">Failed copying {0} to {1}: {2}.</system:String>
     <system:String x:Key="str_ErrFileExistsNotDirFmt">The file {0} exists, but is not a directory.</system:String>
     <system:String x:Key="str_ErrFileGenericCaption">File Error</system:String>
@@ -164,5 +164,6 @@ limitations under the License.
     <system:String x:Key="str_TitleBase">6502bench SourceGen</system:String>
     <system:String x:Key="str_TitleModified">(save needed)</system:String>
     <system:String x:Key="str_TitleNewProject">[new project]</system:String>
+    <system:String x:Key="str_TitleReadOnly">*READ-ONLY*</system:String>
     <system:String x:Key="str_Unset">[unset]</system:String>
 </ResourceDictionary>
\ No newline at end of file
diff --git a/SourceGen/Res/Strings.xaml.cs b/SourceGen/Res/Strings.xaml.cs
index b23891b..168173a 100644
--- a/SourceGen/Res/Strings.xaml.cs
+++ b/SourceGen/Res/Strings.xaml.cs
@@ -309,6 +309,8 @@ namespace SourceGen.Res {
             (string)Application.Current.FindResource("str_TitleModified");
         public static string TITLE_NEW_PROJECT =
             (string)Application.Current.FindResource("str_TitleNewProject");
+        public static string TITLE_READ_ONLY =
+            (string)Application.Current.FindResource("str_TitleReadOnly");
         public static string UNSET =
             (string)Application.Current.FindResource("str_Unset");
     }
diff --git a/SourceGen/RuntimeData/Help/mainwin.html b/SourceGen/RuntimeData/Help/mainwin.html
index adb8276..07c4a57 100644
--- a/SourceGen/RuntimeData/Help/mainwin.html
+++ b/SourceGen/RuntimeData/Help/mainwin.html
@@ -54,8 +54,9 @@ shown.  If it's something simple, like a missing .sym65 or extension
 script file, you'll be notified.  If it's something more complicated,
 e.g. the project has a comment on an offset that doesn't exist, you
 will be warned that the problematic data has been deleted, and will be
-lost if the project is saved.  You will also be given the opportunity
-to cancel the loading of the project.</p>
+lost if the project is saved.  By default, such a project will be opened
+in read-only mode, though you can override this in the dialog.  You will
+also be given the opportunity to simply cancel loading the project.</p>
 
 <p>The locations of the last few projects you've worked with are saved
 in the application settings.  You can access them from
diff --git a/SourceGen/WpfGui/MainWindow.xaml b/SourceGen/WpfGui/MainWindow.xaml
index 66ef0f3..9fdc345 100644
--- a/SourceGen/WpfGui/MainWindow.xaml
+++ b/SourceGen/WpfGui/MainWindow.xaml
@@ -264,9 +264,9 @@ limitations under the License.
         <CommandBinding Command="{StaticResource RedoCmd}"
                         CanExecute="CanRedo" Executed="RedoCmd_Executed"/>
         <CommandBinding Command="Save"
-                        CanExecute="IsProjectOpen" Executed="SaveCmd_Executed"/>
+                        CanExecute="CanSaveProject" Executed="SaveCmd_Executed"/>
         <CommandBinding Command="SaveAs"
-                        CanExecute="IsProjectOpen" Executed="SaveAsCmd_Executed"/>
+                        CanExecute="CanSaveProject" Executed="SaveAsCmd_Executed"/>
         <!-- ListView has a built-in Ctrl+A handler; this only fires when codeListView is not in focus -->
         <CommandBinding Command="{StaticResource SelectAllCmd}"
                         CanExecute="IsProjectOpen" Executed="SelectAllCmd_Executed"/>
diff --git a/SourceGen/WpfGui/MainWindow.xaml.cs b/SourceGen/WpfGui/MainWindow.xaml.cs
index 100d3c9..801ef36 100644
--- a/SourceGen/WpfGui/MainWindow.xaml.cs
+++ b/SourceGen/WpfGui/MainWindow.xaml.cs
@@ -934,7 +934,7 @@ namespace SourceGen.WpfGui {
         /// </summary>
         /// <returns></returns>
         private bool IsProjectOpen() {
-            return mMainCtrl != null && mMainCtrl.IsProjectOpen();
+            return mMainCtrl != null && mMainCtrl.IsProjectOpen;
         }
 
         /// <summary>
@@ -1033,6 +1033,11 @@ namespace SourceGen.WpfGui {
                 (counts.mCodeHints != 0 || counts.mDataHints != 0 || counts.mInlineDataHints != 0);
         }
 
+        private void CanSaveProject(object sender, CanExecuteRoutedEventArgs e) {
+            e.CanExecute = mMainCtrl != null && mMainCtrl.IsProjectOpen &&
+                !mMainCtrl.IsProjectReadOnly;
+        }
+
         private void CanToggleSingleByteFormat(object sender, CanExecuteRoutedEventArgs e) {
             e.CanExecute = IsProjectOpen() && mMainCtrl.CanToggleSingleByteFormat();
         }
diff --git a/SourceGen/WpfGui/ProjectLoadIssues.xaml b/SourceGen/WpfGui/ProjectLoadIssues.xaml
index c9299b4..27b8664 100644
--- a/SourceGen/WpfGui/ProjectLoadIssues.xaml
+++ b/SourceGen/WpfGui/ProjectLoadIssues.xaml
@@ -25,14 +25,23 @@ limitations under the License.
         SizeToContent="WidthAndHeight" ResizeMode="NoResize"
         ShowInTaskbar="False" WindowStartupLocation="CenterOwner"
         Loaded="ProjectLoadIssues_Loaded">
+
+    <Window.Resources>
+        <BooleanToVisibilityConverter x:Key="BoolToVis"/>
+    </Window.Resources>
+
     <DockPanel LastChildFill="False" Margin="8">
         <TextBlock DockPanel.Dock="Top">Problems were detected while loading the project file:</TextBlock>
         <TextBox Name="messageTextBox" DockPanel.Dock="Top" Margin="0,8,0,0"
                  Width="540" Height="110" IsReadOnly="True" TextWrapping="Wrap" Text=""
                  VerticalScrollBarVisibility="Auto"/>
-        <TextBlock Name="invalidDiscardLabel" DockPanel.Dock="Top" Margin="0,8,0,0" Foreground="Red">
+        <TextBlock Name="invalidDiscardLabel" DockPanel.Dock="Top" Margin="0,8,0,0" Foreground="Red"
+                   Visibility="{Binding ShowItemWarning, Converter={StaticResource BoolToVis}}">
             Invalid data items will be discarded when you save the project.
         </TextBlock>
+        <CheckBox Content="Open project in read-only mode" DockPanel.Dock="Top" Margin="0,4,0,0"
+                  IsChecked="{Binding WantReadOnly}"
+                  Visibility="{Binding ShowSaveWarning, Converter={StaticResource BoolToVis}}"/>
         <StackPanel DockPanel.Dock="Bottom" Margin="0,8,0,0"
                     Orientation="Horizontal" HorizontalAlignment="Right">
             <Button Name="okButton" Width="70" Content="Continue" IsDefault="True" Click="OkButton_Click"/>
diff --git a/SourceGen/WpfGui/ProjectLoadIssues.xaml.cs b/SourceGen/WpfGui/ProjectLoadIssues.xaml.cs
index d604854..31ead87 100644
--- a/SourceGen/WpfGui/ProjectLoadIssues.xaml.cs
+++ b/SourceGen/WpfGui/ProjectLoadIssues.xaml.cs
@@ -14,13 +14,28 @@
  * limitations under the License.
  */
 using System;
+using System.ComponentModel;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Windows;
 
 namespace SourceGen.WpfGui {
     /// <summary>
     /// Display errors and warnings generated while attempting to open a project.
     /// </summary>
-    public partial class ProjectLoadIssues : Window {
+    public partial class ProjectLoadIssues : Window, INotifyPropertyChanged {
+        public bool WantReadOnly {
+            get { return mWantReadOnly; }
+            set { mWantReadOnly = value; OnPropertyChanged(); }
+        }
+        private bool mWantReadOnly;
+
+        public bool ShowSaveWarning {
+            get { return mShowItemWarning; }
+            set { mShowItemWarning = value; OnPropertyChanged(); }
+        }
+        private bool mShowItemWarning;
+
         /// <summary>
         /// Multi-line message for text box.
         /// </summary>
@@ -35,10 +50,17 @@ namespace SourceGen.WpfGui {
             Unknown = 0, Continue, Cancel, ContinueOrCancel
         }
 
+        // INotifyPropertyChanged implementation
+        public event PropertyChangedEventHandler PropertyChanged;
+        private void OnPropertyChanged([CallerMemberName] string propertyName = "") {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+
 
         public ProjectLoadIssues(Window owner, string msgs, Buttons allowedButtons) {
             InitializeComponent();
             Owner = owner;
+            DataContext = this;
 
             mMessages = msgs;
             mAllowedButtons = allowedButtons;
@@ -52,14 +74,18 @@ namespace SourceGen.WpfGui {
                 okButton.IsEnabled = false;
 
                 // No point warning them about invalid data if they can't continue.
-                invalidDiscardLabel.Visibility = Visibility.Hidden;
-            }
-            if (mAllowedButtons == Buttons.Continue) {
+                ShowSaveWarning = false;
+            } else if (mAllowedButtons == Buttons.Continue) {
                 // Cancel not allowed.
                 cancelButton.IsEnabled = false;
 
-                // They're stuck with the problem.
-                invalidDiscardLabel.Visibility = Visibility.Hidden;
+                // Problem is outside the scope of the project (e.g. bad platform symbol file),
+                // so saving the project won't change anything.
+                ShowSaveWarning = false;
+            } else {
+                Debug.Assert(mAllowedButtons == Buttons.ContinueOrCancel);
+                ShowSaveWarning = true;
+                WantReadOnly = true;
             }
         }