diff --git a/src/osgEarth/ObjectIDPicker b/src/osgEarth/ObjectIDPicker
index 8358bfa261..45c985f63e 100644
--- a/src/osgEarth/ObjectIDPicker
+++ b/src/osgEarth/ObjectIDPicker
@@ -53,6 +53,10 @@ namespace osgEarth { namespace Util
         void setBuffer(int value) { _buffer = value; }
         int getBuffer() const { return _buffer; }
 
+        //! Size of the RTT image (pixels per side) - must call before setView()
+        void setRTTSize(int value) { _rttSize = value; }
+        int getRTTSize() const { return _rttSize; }
+
         using Function = std::function<void(ObjectID)>;
 
         //! Function to call when the user hovers an object
diff --git a/src/osgEarth/ObjectIDPicker.cpp b/src/osgEarth/ObjectIDPicker.cpp
index 1ad6c997d2..5c5e0752dc 100644
--- a/src/osgEarth/ObjectIDPicker.cpp
+++ b/src/osgEarth/ObjectIDPicker.cpp
@@ -105,6 +105,8 @@ ObjectIDPicker::~ObjectIDPicker()
 void
 ObjectIDPicker::setView(osgViewer::View* view)
 {
+    OE_SOFT_ASSERT_AND_RETURN(_rttSize >= 1, void());
+
     if (view != _view.get())
     {
         _view = view;