diff --git a/gatelock/gatelock/_fitcheck.py b/gatelock/gatelock/_fitcheck.py
index e5b2196..ed40a19 100644
--- a/gatelock/gatelock/_fitcheck.py
+++ b/gatelock/gatelock/_fitcheck.py
@@ -109,6 +109,13 @@ def _measure(
     """Render the screen once and read its height back."""
     root = tk.Tk()
     try:
+        # A managed window has its geometry rewritten wholesale by a real
+        # window manager -- confirmed under i3, which tiled this to the pane
+        # size instead of the requested width/height, silently measuring the
+        # wrong resolution. Production lock windows are overrideredirect for
+        # exactly this reason; the throwaway root here must match so the
+        # measurement is honest regardless of what WM is running the check.
+        root.overrideredirect(boolean=True)
         root.geometry(f"{width}x{height}+0+0")
         root.update_idletasks()
         surface = ScrollableSurface(root, config or LockConfig(), center_when_fits=True)
diff --git a/gatelock/gatelock/tests/test_scrollable.py b/gatelock/gatelock/tests/test_scrollable.py
index 6964207..cd17439 100644
--- a/gatelock/gatelock/tests/test_scrollable.py
+++ b/gatelock/gatelock/tests/test_scrollable.py
@@ -35,6 +35,12 @@ _TALL = 60
 def surface() -> tk.Misc:
     """A 400x200 viewport holding 20 stacked entries -- deliberately taller."""
     root = tk.Tk()
+    # A managed window has its geometry rewritten wholesale by a real window
+    # manager (i3 confirmed: a plain geometry() request came back tiled to
+    # the pane size instead of 400x200, so nothing ever overflowed and every
+    # scroll assertion in this file failed against a real WM session) --
+    # exactly the reason production lock windows are overrideredirect too.
+    root.overrideredirect(boolean=True)
     root.geometry(f"400x{_VIEWPORT_H}+0+0")
     # No window manager under Xvfb, so the toplevel must claim X input focus
     # before any synthetic key event is delivered anywhere.
@@ -203,6 +209,9 @@ def test_a_surface_without_a_scrollbar_still_scrolls() -> None:
     """``show_scrollbar=False`` removes the affordance, not the mechanism."""
     root = tk.Tk()
     try:
+        # See the `surface` fixture above for why this must be
+        # overrideredirect under a real WM.
+        root.overrideredirect(boolean=True)
         root.geometry(f"400x{_VIEWPORT_H}+0+0")
         root.focus_force()
         root.update_idletasks()
diff --git a/gatelock/pyproject.toml b/gatelock/pyproject.toml
index 1ceade6..93608e9 100644
--- a/gatelock/pyproject.toml
+++ b/gatelock/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "gatelock"
-version = "0.7.0"
+version = "0.7.1"
 description = "Shared per-output lock-window + HMAC log-integrity backend for blocking-overlay apps"
 requires-python = ">=3.10"
 dependencies = []  # pure stdlib — tkinter is bundled with Python