diff --git a/packages/ludic.zones/README.md b/packages/ludic.zones/README.md
index 979d7f82..e4ae25cd 100644
--- a/packages/ludic.zones/README.md
+++ b/packages/ludic.zones/README.md
@@ -1,7 +1,7 @@
 # ludic.zones
 
 Where a world is simulated: a disc per player - `(x, z, r)`, `r = zones_radius(fog)`, that is the
-fog distance plus 40 m and never under 150 m, 900 m with no fog - and the discs that overlap merged
+fog distance plus 40 m, never under 150 m nor over 900 m, and 900 m with no fog - and the discs that overlap merged
 into clusters with a bounding circle. Uses `ludic.base` and nothing else.
 
 - `zones_set(pid, x, z, r)`, `zones_clear(pid)`, `zones_reset()`; `zones_merge()` once a frame
diff --git a/packages/ludic.zones/state.ludic b/packages/ludic.zones/state.ludic
index 48a76c6e..6ea8fba4 100644
--- a/packages/ludic.zones/state.ludic
+++ b/packages/ludic.zones/state.ludic
@@ -18,10 +18,11 @@ export state ZonesState {
   zn_cn: words = words(ZONES_MAX)             # how many discs it holds
 }
 
-# a player's radius from how far they see: fog_dist <= 0 is no fog
+# a player's radius from how far they see: fog_dist <= 0 is no fog; never past no fog's, so a far fog
+# never keeps more of the world than none does
 export function zones_radius(fog_dist: float) -> float {
   if fog_dist <= 0.0 { return ZONES_NO_FOG }
-  return Math.max(fog_dist + ZONES_PAST_FOG, ZONES_LEAST)
+  return Math.min(Math.max(fog_dist + ZONES_PAST_FOG, ZONES_LEAST), ZONES_NO_FOG)
 }
 
 export function zones_set(zones_st: mut ZonesState, pid: int, x: float, z: float, r: float) -> void {
diff --git a/packages/ludic.zones/tests/zones_test.ludic b/packages/ludic.zones/tests/zones_test.ludic
index 1206f13b..a8348ea3 100644
--- a/packages/ludic.zones/tests/zones_test.ludic
+++ b/packages/ludic.zones/tests/zones_test.ludic
@@ -44,9 +44,11 @@ program ZonesTest {
     expect(Math.abs(zones_nearest(zones_st, 350.0, 100.0) - 100.0) < 0.001)
   }
 
-  test "a player's radius: past the fog, never under the least, the horizon with none" (zones_st: mut ZonesState) {
+  test "a player's radius: past the fog, never under the least nor over no fog's" (zones_st: mut ZonesState) {
     expect(zones_radius(0.0) == ZONES_NO_FOG)
     expect(zones_radius(30.0) == ZONES_LEAST)
     expect(zones_radius(500.0) == 540.0)
+    expect(zones_radius(1000.0) == ZONES_NO_FOG)     # a kilometre's fog keeps no more than none
+    expect(zones_radius(860.0) == ZONES_NO_FOG)
   }
 }