diff --git a/Code/Sandbox/Editor/CryEdit.cpp b/Code/Sandbox/Editor/CryEdit.cpp
index c723e6049a..a972a4bd9b 100644
--- a/Code/Sandbox/Editor/CryEdit.cpp
+++ b/Code/Sandbox/Editor/CryEdit.cpp
@@ -2281,6 +2281,14 @@ int CCryEditApp::IdleProcessing(bool bBackgroundUpdate)
         return 0;
     }
 
+    // Ensure we don't get called re-entrantly
+    // This can occur when a nested Qt event loop fires (e.g. by way of a modal dialog calling exec)
+    if (m_idleProcessingRunning)
+    {
+        return 0;
+    }
+    QScopedValueRollback<bool> guard(m_idleProcessingRunning, true);
+
     ////////////////////////////////////////////////////////////////////////
     // Call the update function of the engine
     ////////////////////////////////////////////////////////////////////////
diff --git a/Code/Sandbox/Editor/CryEdit.h b/Code/Sandbox/Editor/CryEdit.h
index dc4f015faf..e37fb53561 100644
--- a/Code/Sandbox/Editor/CryEdit.h
+++ b/Code/Sandbox/Editor/CryEdit.h
@@ -335,6 +335,8 @@ private:
     // If this flag is set, the next OnIdle() will update, even if the app is in the background, and then
     // this flag will be reset.
     bool m_bForceProcessIdle = false;
+    // This is set while IdleProcessing is running to prevent re-entrancy
+    bool m_idleProcessingRunning = false;
     // Keep the editor alive, even if no focus is set
     bool m_bKeepEditorActive = false;
     // Currently creating a new level