diff --git a/rfg_vna_viewer.py b/rfg_vna_viewer.py
index c55b2cf..4917745 100644
--- a/rfg_vna_viewer.py
+++ b/rfg_vna_viewer.py
@@ -283,11 +283,14 @@ def make_update(reader, parser, assembler, curves, plots):
         fft_db = 20.0 * np.log10(fft_mag + 1e-12)
         c_fft.setData(fft_dist, fft_db)
 
-        # Lock axes after first sweep
+        # Lock axes after first sweep — freeze current Y ranges
         if not state["axes_locked"]:
             state["axes_locked"] = True
             for p in plots:
-                p.enableAutoRange(False)
+                vr = p.viewRange()
+                p.disableAutoRange()
+                p.setXRange(vr[0][0], vr[0][1], padding=0)
+                p.setYRange(vr[1][0], vr[1][1], padding=0)
 
     return update