diff --git a/extras/Projucer/Source/Project/Modules/jucer_Modules.cpp b/extras/Projucer/Source/Project/Modules/jucer_Modules.cpp
index 1b80d8695d..ebc0bcdccb 100644
--- a/extras/Projucer/Source/Project/Modules/jucer_Modules.cpp
+++ b/extras/Projucer/Source/Project/Modules/jucer_Modules.cpp
@@ -411,6 +411,8 @@ void EnabledModulesList::sortAlphabetically()
     };
 
     ModuleTreeSorter sorter;
+
+    const ScopedLock sl (stateLock);
     state.sort (sorter, getUndoManager(), false);
 }
 
@@ -439,6 +441,7 @@ ModuleDescription EnabledModulesList::getModuleInfo (const String& moduleID) con
 
 bool EnabledModulesList::isModuleEnabled (const String& moduleID) const
 {
+    const ScopedLock sl (stateLock);
     return state.getChildWithProperty (Ids::ID, moduleID).isValid();
 }
 
@@ -502,11 +505,13 @@ bool EnabledModulesList::doesModuleHaveHigherCppStandardThanProject (const Strin
 
 bool EnabledModulesList::shouldUseGlobalPath (const String& moduleID) const
 {
+    const ScopedLock sl (stateLock);
     return (bool) shouldUseGlobalPathValue (moduleID).getValue();
 }
 
 Value EnabledModulesList::shouldUseGlobalPathValue (const String& moduleID) const
 {
+    const ScopedLock sl (stateLock);
     return state.getChildWithProperty (Ids::ID, moduleID)
                 .getPropertyAsValue (Ids::useGlobalPath, getUndoManager());
 }
@@ -518,6 +523,7 @@ bool EnabledModulesList::shouldShowAllModuleFilesInProject (const String& module
 
 Value EnabledModulesList::shouldShowAllModuleFilesInProjectValue (const String& moduleID) const
 {
+    const ScopedLock sl (stateLock);
     return state.getChildWithProperty (Ids::ID, moduleID)
                 .getPropertyAsValue (Ids::showAllCode, getUndoManager());
 }
@@ -529,6 +535,7 @@ bool EnabledModulesList::shouldCopyModuleFilesLocally (const String& moduleID) c
 
 Value EnabledModulesList::shouldCopyModuleFilesLocallyValue (const String& moduleID) const
 {
+    const ScopedLock sl (stateLock);
     return state.getChildWithProperty (Ids::ID, moduleID)
                 .getPropertyAsValue (Ids::useLocalCopy, getUndoManager());
 }
@@ -616,7 +623,11 @@ void EnabledModulesList::addModule (const File& moduleFolder, bool copyLocally,
             ValueTree module (Ids::MODULE);
             module.setProperty (Ids::ID, moduleID, getUndoManager());
 
-            state.appendChild (module, getUndoManager());
+            {
+                const ScopedLock sl (stateLock);
+                state.appendChild (module, getUndoManager());
+            }
+
             sortAlphabetically();
 
             shouldShowAllModuleFilesInProjectValue (moduleID) = true;
@@ -686,9 +697,13 @@ void EnabledModulesList::addModuleOfferingToCopy (const File& f, bool isFromUser
 
 void EnabledModulesList::removeModule (String moduleID) // must be pass-by-value, and not a const ref!
 {
-    for (auto i = state.getNumChildren(); --i >= 0;)
-        if (state.getChild(i) [Ids::ID] == moduleID)
-            state.removeChild (i, getUndoManager());
+    {
+        const ScopedLock sl (stateLock);
+
+        for (auto i = state.getNumChildren(); --i >= 0;)
+            if (state.getChild(i) [Ids::ID] == moduleID)
+                state.removeChild (i, getUndoManager());
+    }
 
     for (Project::ExporterIterator exporter (project); exporter.next();)
         exporter->removePathForModule (moduleID);
diff --git a/extras/Projucer/Source/Project/Modules/jucer_Modules.h b/extras/Projucer/Source/Project/Modules/jucer_Modules.h
index 8d3e54bceb..c75272bc3e 100644
--- a/extras/Projucer/Source/Project/Modules/jucer_Modules.h
+++ b/extras/Projucer/Source/Project/Modules/jucer_Modules.h
@@ -138,6 +138,8 @@ private:
     UndoManager* getUndoManager() const     { return project.getUndoManagerFor (state); }
 
     Project& project;
+
+    CriticalSection stateLock;
     ValueTree state;
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (EnabledModulesList)