diff --git a/README.md b/README.md
index c8cb62d9..d3292e2a 100644
--- a/README.md
+++ b/README.md
@@ -40,8 +40,8 @@ projects % git clone git@github.com:nworbmot/pypsa-eur-sec.git
 
 The requirements are the same as
 [PyPSA-Eur](https://github.com/PyPSA/pypsa-eur), but for
-`solve_network.py` in addition you need `gurobipy` and version
->=0.16.0 of PyPSA in order to use the `nomopyomo` framework. These
+`solve_network.py` in addition you need `gurobipy` and version 0.16.0
+or greater of PyPSA in order to use the `nomopyomo` framework. These
 libraries are currently imported "by hand" at the start of the
 `solve_network.py` script.
 
diff --git a/scripts/prepare_sector_network.py b/scripts/prepare_sector_network.py
index 508e51ee..fb2a2cce 100644
--- a/scripts/prepare_sector_network.py
+++ b/scripts/prepare_sector_network.py
@@ -540,7 +540,8 @@ def add_storage(network):
     connector = " -> "
     attrs = ["bus0","bus1","length"]
 
-    candidates = pd.concat([n.lines[attrs],n.links.loc[n.links.carrier == "DC",attrs]])
+    candidates = pd.concat([n.lines[attrs],n.links.loc[n.links.carrier == "DC",attrs]],
+                           keys=["lines","links"])
 
     for candidate in candidates.index:
         buses = [candidates.at[candidate,"bus0"],candidates.at[candidate,"bus1"]]