diff --git a/libraries/script-engine/src/ScriptEngine.cpp b/libraries/script-engine/src/ScriptEngine.cpp
index 7f2a992f68..cfd155e14b 100644
--- a/libraries/script-engine/src/ScriptEngine.cpp
+++ b/libraries/script-engine/src/ScriptEngine.cpp
@@ -1974,8 +1974,9 @@ void ScriptEngine::forwardHandlerCall(const EntityItemID& entityID, const QStrin
 }
 
 int ScriptEngine::getNumRunningEntityScripts() const {
+    QReadLocker locker { &_entityScriptsLock };
     int sum = 0;
-    for (auto& st : _entityScripts) {
+    for (const auto& st : _entityScripts) {
         if (st.status == EntityScriptStatus::RUNNING) {
             ++sum;
         }
@@ -1984,14 +1985,20 @@ int ScriptEngine::getNumRunningEntityScripts() const {
 }
 
 void ScriptEngine::setEntityScriptDetails(const EntityItemID& entityID, const EntityScriptDetails& details) {
-    _entityScripts[entityID] = details;
+    {
+        QWriteLocker locker { &_entityScriptsLock };
+        _entityScripts[entityID] = details;
+    }
     emit entityScriptDetailsUpdated();
 }
 
 void ScriptEngine::updateEntityScriptStatus(const EntityItemID& entityID, const EntityScriptStatus &status, const QString& errorInfo) {
-    EntityScriptDetails &details = _entityScripts[entityID];
-    details.status = status;
-    details.errorInfo = errorInfo;
+    {
+        QWriteLocker locker { &_entityScriptsLock };
+        EntityScriptDetails& details = _entityScripts[entityID];
+        details.status = status;
+        details.errorInfo = errorInfo;
+    }
     emit entityScriptDetailsUpdated();
 }
 
@@ -2042,6 +2049,7 @@ QFuture<QVariant> ScriptEngine::getLocalEntityScriptDetails(const EntityItemID&
 }
 
 bool ScriptEngine::getEntityScriptDetails(const EntityItemID& entityID, EntityScriptDetails &details) const {
+    QReadLocker locker { &_entityScriptsLock };
     auto it = _entityScripts.constFind(entityID);
     if (it == _entityScripts.constEnd()) {
         return false;
@@ -2050,6 +2058,11 @@ bool ScriptEngine::getEntityScriptDetails(const EntityItemID& entityID, EntitySc
     return true;
 }
 
+bool ScriptEngine::hasEntityScriptDetails(const EntityItemID& entityID) const {
+    QReadLocker locker { &_entityScriptsLock };
+    return _entityScripts.contains(entityID);
+}
+
 const static EntityItemID BAD_SCRIPT_UUID_PLACEHOLDER { "{20170224-dead-face-0000-cee000021114}" };
 
 void ScriptEngine::processDeferredEntityLoads(const QString& entityScript, const EntityItemID& leaderID) {
@@ -2064,14 +2077,15 @@ void ScriptEngine::processDeferredEntityLoads(const QString& entityScript, const
     }
     foreach(DeferredLoadEntity retry, retryLoads) {
         // check whether entity was since been deleted
-        if (!_entityScripts.contains(retry.entityID)) {
+
+        EntityScriptDetails details;
+        if (!getEntityScriptDetails(retry.entityID, details)) {
             qCDebug(scriptengine) << "processDeferredEntityLoads -- entity details gone (entity deleted?)"
                                   << retry.entityID;
             continue;
         }
 
         // check whether entity has since been unloaded or otherwise errored-out
-        auto details = _entityScripts[retry.entityID];
         if (details.status != EntityScriptStatus::PENDING) {
             qCDebug(scriptengine) << "processDeferredEntityLoads -- entity status no longer PENDING; "
                                   << retry.entityID << details.status;
@@ -2079,7 +2093,11 @@ void ScriptEngine::processDeferredEntityLoads(const QString& entityScript, const
         }
 
         // propagate leader's failure reasons to the pending entity
-        const auto leaderDetails = _entityScripts[leaderID];
+        EntityScriptDetails leaderDetails;
+        {
+            QWriteLocker locker { &_entityScriptsLock };
+            leaderDetails = _entityScripts[leaderID];
+        }
         if (leaderDetails.status != EntityScriptStatus::RUNNING) {
             qCDebug(scriptengine) << QString("... pending load of %1 cancelled (leader: %2 status: %3)")
                 .arg(retry.entityID.toString()).arg(leaderID.toString()).arg(leaderDetails.status);
@@ -2125,7 +2143,7 @@ void ScriptEngine::loadEntityScript(const EntityItemID& entityID, const QString&
         return;
     }
 
-    if (!_entityScripts.contains(entityID)) {
+    if (!hasEntityScriptDetails(entityID)) {
         // make sure EntityScriptDetails has an entry for this UUID right away
         // (which allows bailing from the loading/provisioning process early if the Entity gets deleted mid-flight)
         updateEntityScriptStatus(entityID, EntityScriptStatus::PENDING, "...pending...");
@@ -2166,9 +2184,12 @@ void ScriptEngine::loadEntityScript(const EntityItemID& entityID, const QString&
     _occupiedScriptURLs[entityScript] = entityID;
 
 #ifdef DEBUG_ENTITY_STATES
-    auto previousStatus = _entityScripts.contains(entityID) ? _entityScripts[entityID].status : EntityScriptStatus::PENDING;
-    qCDebug(scriptengine) << "loadEntityScript.LOADING: " << entityScript << entityID.toString()
-                                 << "(previous: " << previousStatus << ")";
+    {
+        EntityScriptDetails details;
+        bool hasEntityScript = getEntityScriptDetails(entityID, details);
+        qCDebug(scriptengine) << "loadEntityScript.LOADING: " << entityScript << entityID.toString()
+            << "(previous: " << (hasEntityScript ? details.status : EntityScriptStatus::PENDING) << ")";
+    }
 #endif
 
     EntityScriptDetails newDetails;
@@ -2197,7 +2218,7 @@ void ScriptEngine::loadEntityScript(const EntityItemID& entityID, const QString&
 #ifdef DEBUG_ENTITY_STATES
                 qCDebug(scriptengine) << "loadEntityScript.contentAvailable" << status << QUrl(url).fileName() << entityID.toString();
 #endif
-                if (!isStopping() && _entityScripts.contains(entityID)) {
+                if (!isStopping() && hasEntityScriptDetails(entityID)) {
                     _contentAvailableQueue[entityID] = { entityID, url, contents, isURL, success, status };
                 } else {
 #ifdef DEBUG_ENTITY_STATES
@@ -2267,8 +2288,11 @@ void ScriptEngine::entityScriptContentAvailable(const EntityItemID& entityID, co
     bool isFileUrl = isURL && scriptOrURL.startsWith("file://");
     auto fileName = isURL ? scriptOrURL : "about:EmbeddedEntityScript";
 
-    const EntityScriptDetails &oldDetails = _entityScripts[entityID];
-    const QString entityScript = oldDetails.scriptText;
+    QString entityScript;
+    {
+        QWriteLocker locker { &_entityScriptsLock };
+        entityScript = _entityScripts[entityID].scriptText;
+    }
 
     EntityScriptDetails newDetails;
     newDetails.scriptText = scriptOrURL;
@@ -2446,8 +2470,8 @@ void ScriptEngine::unloadEntityScript(const EntityItemID& entityID, bool shouldR
         "entityID:" << entityID;
 #endif
 
-    if (_entityScripts.contains(entityID)) {
-        const EntityScriptDetails &oldDetails = _entityScripts[entityID];
+    EntityScriptDetails oldDetails;
+    if (getEntityScriptDetails(entityID, oldDetails)) {
         auto scriptText = oldDetails.scriptText;
 
         if (isEntityScriptRunning(entityID)) {
@@ -2460,7 +2484,10 @@ void ScriptEngine::unloadEntityScript(const EntityItemID& entityID, bool shouldR
 #endif
         if (shouldRemoveFromMap) {
             // this was a deleted entity, we've been asked to remove it from the map
-            _entityScripts.remove(entityID);
+            {
+                QWriteLocker locker { &_entityScriptsLock };
+                _entityScripts.remove(entityID);
+            }
             emit entityScriptDetailsUpdated();
         } else if (oldDetails.status != EntityScriptStatus::UNLOADED) {
             EntityScriptDetails newDetails;
@@ -2491,10 +2518,19 @@ void ScriptEngine::unloadAllEntityScripts() {
 #ifdef THREAD_DEBUGGING
     qCDebug(scriptengine) << "ScriptEngine::unloadAllEntityScripts() called on correct thread [" << thread() << "]";
 #endif
-    foreach(const EntityItemID& entityID, _entityScripts.keys()) {
+
+    QList<EntityItemID> keys;
+    {
+        QReadLocker locker{ &_entityScriptsLock };
+        keys = _entityScripts.keys();
+    }
+    foreach(const EntityItemID& entityID, keys) {
         unloadEntityScript(entityID);
     }
-    _entityScripts.clear();
+    {
+        QWriteLocker locker{ &_entityScriptsLock };
+        _entityScripts.clear();
+    }
     emit entityScriptDetailsUpdated();
     _occupiedScriptURLs.clear();
 
@@ -2508,7 +2544,7 @@ void ScriptEngine::unloadAllEntityScripts() {
 }
 
 void ScriptEngine::refreshFileScript(const EntityItemID& entityID) {
-    if (!HIFI_AUTOREFRESH_FILE_SCRIPTS || !_entityScripts.contains(entityID)) {
+    if (!HIFI_AUTOREFRESH_FILE_SCRIPTS || !hasEntityScriptDetails(entityID)) {
         return;
     }
 
@@ -2518,7 +2554,11 @@ void ScriptEngine::refreshFileScript(const EntityItemID& entityID) {
     }
     recurseGuard = true;
 
-    EntityScriptDetails details = _entityScripts[entityID];
+    EntityScriptDetails details;
+    {
+        QWriteLocker locker { &_entityScriptsLock };
+        details = _entityScripts[entityID];
+    }
     // Check to see if a file based script needs to be reloaded (easier debugging)
     if (details.lastModified > 0) {
         QString filePath = QUrl(details.scriptText).toLocalFile();
@@ -2584,7 +2624,11 @@ void ScriptEngine::callEntityScriptMethod(const EntityItemID& entityID, const QS
         refreshFileScript(entityID);
     }
     if (isEntityScriptRunning(entityID)) {
-        EntityScriptDetails details = _entityScripts[entityID];
+        EntityScriptDetails details;
+        {
+            QWriteLocker locker { &_entityScriptsLock };
+            details = _entityScripts[entityID];
+        }
         QScriptValue entityScript = details.scriptObject; // previously loaded
 
         // If this is a remote call, we need to check to see if the function is remotely callable
@@ -2646,7 +2690,11 @@ void ScriptEngine::callEntityScriptMethod(const EntityItemID& entityID, const QS
         refreshFileScript(entityID);
     }
     if (isEntityScriptRunning(entityID)) {
-        EntityScriptDetails details = _entityScripts[entityID];
+        EntityScriptDetails details;
+        {
+            QWriteLocker locker { &_entityScriptsLock };
+            details = _entityScripts[entityID];
+        }
         QScriptValue entityScript = details.scriptObject; // previously loaded
         if (entityScript.property(methodName).isFunction()) {
             QScriptValueList args;
@@ -2680,7 +2728,11 @@ void ScriptEngine::callEntityScriptMethod(const EntityItemID& entityID, const QS
         refreshFileScript(entityID);
     }
     if (isEntityScriptRunning(entityID)) {
-        EntityScriptDetails details = _entityScripts[entityID];
+        EntityScriptDetails details;
+        {
+            QWriteLocker locker { &_entityScriptsLock };
+            details = _entityScripts[entityID];
+        }
         QScriptValue entityScript = details.scriptObject; // previously loaded
         if (entityScript.property(methodName).isFunction()) {
             QScriptValueList args;
diff --git a/libraries/script-engine/src/ScriptEngine.h b/libraries/script-engine/src/ScriptEngine.h
index 94b50bfd2c..08e2c492e8 100644
--- a/libraries/script-engine/src/ScriptEngine.h
+++ b/libraries/script-engine/src/ScriptEngine.h
@@ -461,7 +461,9 @@ public:
      * @returns {boolean}
      */
     Q_INVOKABLE bool isEntityScriptRunning(const EntityItemID& entityID) {
-        return _entityScripts.contains(entityID) && _entityScripts[entityID].status == EntityScriptStatus::RUNNING;
+        QReadLocker locker { &_entityScriptsLock };
+        auto it = _entityScripts.constFind(entityID);
+        return it != _entityScripts.constEnd() && it->status == EntityScriptStatus::RUNNING;
     }
     QVariant cloneEntityScriptDetails(const EntityItemID& entityID);
     QFuture<QVariant> getLocalEntityScriptDetails(const EntityItemID& entityID) override;
@@ -559,6 +561,7 @@ public:
     void clearDebugLogWindow();
     int getNumRunningEntityScripts() const;
     bool getEntityScriptDetails(const EntityItemID& entityID, EntityScriptDetails &details) const;
+    bool hasEntityScriptDetails(const EntityItemID& entityID) const;
 
 public slots:
 
@@ -771,6 +774,7 @@ protected:
     bool _isInitialized { false };
     QHash<QTimer*, CallbackData> _timerFunctionMap;
     QSet<QUrl> _includedURLs;
+    mutable QReadWriteLock _entityScriptsLock { QReadWriteLock::Recursive };
     QHash<EntityItemID, EntityScriptDetails> _entityScripts;
     QHash<QString, EntityItemID> _occupiedScriptURLs;
     QList<DeferredLoadEntity> _deferredEntityLoads;