diff --git a/doc/release_notes.md b/doc/release_notes.md
index 79c6bf77cc..00f2e3b6ac 100644
--- a/doc/release_notes.md
+++ b/doc/release_notes.md
@@ -43,6 +43,8 @@
 
 * Introduce SBOM/Grype vulnerability scanning workflow, as a follow-up to the [upstream addition](https://github.com/PyPSA/pypsa-eur/pull/2164) ([754](https://github.com/open-energy-transition/open-tyndp/pull/754)).
 
+* Ensure `inflow_t` is always defined in `attach_hydro`, resolving a pylint use-before-assignment issue ([777](https://github.com/open-energy-transition/open-tyndp/pull/777)).
+
 
 ## Upcoming PyPSA-Eur Release
 * Security: SBOM security scan included in CI.
diff --git a/scripts/add_electricity.py b/scripts/add_electricity.py
index 3d324a6d76..efe64b62e0 100755
--- a/scripts/add_electricity.py
+++ b/scripts/add_electricity.py
@@ -878,6 +878,7 @@ def attach_hydro(
     country = ppl["bus"].map(n.buses.country).rename("country")
 
     inflow_idx = ror.index.union(hydro.index)
+    inflow_t = pd.DataFrame()
     if not inflow_idx.empty:
         dist_key = ppl.loc[inflow_idx, "p_nom"].groupby(country).transform(normed)
 
@@ -911,7 +912,7 @@ def attach_hydro(
             capital_cost=costs.at["ror", "capital_cost"],
             weight=ror["p_nom"],
             p_max_pu=(
-                inflow_t[ror.index]  # pylint: disable=E0606
+                inflow_t[ror.index]
                 .divide(ror["p_nom"], axis=1)
                 .where(lambda df: df <= 1.0, other=1.0)
             ),