diff --git a/CHANGELOG.md b/CHANGELOG.md
index 195cffb..f21fffc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,11 @@ Fixes:
   against every cell: for Deggendorf and Koeln in one database that
   took 29 minutes before linking began. Each building's cell is now
   computed from its coordinates; the batches are unchanged.
+- Feature extraction works on PostgreSQL 18. There every batch holding
+  a flat roof or ground surface failed with division by zero in
+  surface_dimensions, so no building was extracted. PostgreSQL 16 and
+  17 were not affected. A database created by an earlier release gets
+  the fixed function on its next -reset-city2tabula.
 
 ## v0.11.4 (2026-10-20)
 
diff --git a/sql/functions/01_surface_area_corrected_geom.sql b/sql/functions/01_surface_area_corrected_geom.sql
index e6c0f6d..6ee3732 100644
--- a/sql/functions/01_surface_area_corrected_geom.sql
+++ b/sql/functions/01_surface_area_corrected_geom.sql
@@ -78,7 +78,9 @@ CREATE FUNCTION {city2tabula_schema}.surface_dimensions(
     WITH axes AS (
         SELECT -ny / h AS ux, nx / h AS uy,
                -nz * nx / h AS vx, -nz * ny / h AS vy, h AS vz
-        FROM (SELECT sqrt(nx * nx + ny * ny) AS h) s
+        -- NULLIF because PostgreSQL 18 computes the axes of a flat face (h = 0)
+        -- before the WHERE below discards it, and raises division by zero.
+        FROM (SELECT NULLIF(sqrt(nx * nx + ny * ny), 0) AS h) s
         WHERE ABS(nz) <= 0.985
     ),
     projected AS (