diff --git a/viewer/windows/JFJochViewerReciprocalSpaceWindow.cpp b/viewer/windows/JFJochViewerReciprocalSpaceWindow.cpp
index 0eb41f23..1c992796 100644
--- a/viewer/windows/JFJochViewerReciprocalSpaceWindow.cpp
+++ b/viewer/windows/JFJochViewerReciprocalSpaceWindow.cpp
@@ -472,6 +472,12 @@ void JFJochViewerReciprocalSpaceWindow::imageLoaded(std::shared_ptr<const JFJoch
     if (full_dataset_mode_)
         return;
 
+    // Closed: skip extracting this frame's spots as well, not just the GL rebuild.
+    if (!isVisible()) {
+        pending_rebuild_ = true;
+        return;
+    }
+
     loadCurrentImageSpots(current_image_);
     rebuildGL();
 }
@@ -619,6 +625,29 @@ QColor JFJochViewerReciprocalSpaceWindow::spotColorFor(bool indexed,
 }
 
 void JFJochViewerReciprocalSpaceWindow::rebuildGL() {
+    // The reciprocal-space view is a gadget that is closed almost all of the time. Building the
+    // vertex arrays and pushing them to the GL view is real work on every frame, and nobody is
+    // looking at the result, so note that a rebuild is owed and do it when the window is shown.
+    if (!isVisible()) {
+        pending_rebuild_ = true;
+        return;
+    }
+    pending_rebuild_ = false;
+    rebuildGLNow();
+}
+
+void JFJochViewerReciprocalSpaceWindow::showEvent(QShowEvent *event) {
+    JFJochHelperWindow::showEvent(event);
+    if (!pending_rebuild_)
+        return;
+    pending_rebuild_ = false;
+    // Spots for the current frame were not extracted while the window was closed either.
+    if (!full_dataset_mode_)
+        loadCurrentImageSpots(current_image_);
+    rebuildGLNow();
+}
+
+void JFJochViewerReciprocalSpaceWindow::rebuildGLNow() {
     const bool crystal_frame = crystalFrameCheck->isChecked() && has_rotation_;
 
     std::optional<CrystalLattice> plot_lattice;
diff --git a/viewer/windows/JFJochViewerReciprocalSpaceWindow.h b/viewer/windows/JFJochViewerReciprocalSpaceWindow.h
index 67d5a6c1..22a3d619 100644
--- a/viewer/windows/JFJochViewerReciprocalSpaceWindow.h
+++ b/viewer/windows/JFJochViewerReciprocalSpaceWindow.h
@@ -143,7 +143,12 @@ private:
     };
 
     QColor spotColorFor(bool indexed, bool ice_ring) const;
+    // rebuildGL() is a no-op while the window is closed - it only records that a rebuild is
+    // owed, and showEvent() pays it. rebuildGLNow() is the actual work.
     void   rebuildGL();   // rebuilds both spot and line vertex data
+    void   rebuildGLNow();
+    void   showEvent(QShowEvent *event) override;
+    bool   pending_rebuild_ = false;
     void   loadCurrentImageSpots(std::shared_ptr<const JFJochReaderImage> image);
     void   addSpot(const SpotToSave &s,
                    const DiffractionGeometry &geom,