diff --git a/doc/release_notes.rst b/doc/release_notes.rst
index ef019ad6..012f1155 100644
--- a/doc/release_notes.rst
+++ b/doc/release_notes.rst
@@ -10,6 +10,8 @@ Release Notes
 Upcoming Release
 ================
 
+* Bugfix to avoid duplicated offshore regions.
+
 * Added option ``industry: HVC_environment_sequestration_fraction:`` to specify
   the fraction of carbon contained plastics that is permanently sequestered in
   landfill. The default assumption is that all carbon contained in plastics is
diff --git a/scripts/base_network.py b/scripts/base_network.py
index 432813cf..870fcf19 100644
--- a/scripts/base_network.py
+++ b/scripts/base_network.py
@@ -569,7 +569,7 @@ def _set_countries_and_substations(n, config, country_shapes, offshore_shapes):
     buses["substation_lv"] = (
         lv_b & onshore_b & (~buses["under_construction"]) & has_connections_b
     )
-    buses["substation_off"] = (offshore_b | (hv_b & onshore_b)) & (
+    buses["substation_off"] = ((hv_b & offshore_b) | (hv_b & onshore_b)) & (
         ~buses["under_construction"]
     )