diff --git a/config/test/config.electricity.yaml b/config/test/config.electricity.yaml
index ef9bfdc0..b750bf62 100644
--- a/config/test/config.electricity.yaml
+++ b/config/test/config.electricity.yaml
@@ -69,8 +69,8 @@ lines:
 
 solving:
   solver:
-    name: highs
-    options: "highs-default"
+    name: glpk
+    options: "glpk-default"
 
 
 plotting:
diff --git a/config/test/config.myopic.yaml b/config/test/config.myopic.yaml
index 1da51b36..2dab7b04 100644
--- a/config/test/config.myopic.yaml
+++ b/config/test/config.myopic.yaml
@@ -73,8 +73,8 @@ industry:
 
 solving:
   solver:
-    name: highs
-    options: highs-default
+    name: glpk
+    options: glpk-default
   mem: 4000
 
 plotting:
diff --git a/config/test/config.overnight.yaml b/config/test/config.overnight.yaml
index dffdab5a..6d1900cf 100644
--- a/config/test/config.overnight.yaml
+++ b/config/test/config.overnight.yaml
@@ -65,8 +65,8 @@ sector:
 
 solving:
   solver:
-    name: highs
-    options: highs-default
+    name: glpk
+    options: glpk-default
   mem: 4000
 
 plotting:
diff --git a/config/test/config.perfect.yaml b/config/test/config.perfect.yaml
index 8a5a9cce..f20a2c9f 100644
--- a/config/test/config.perfect.yaml
+++ b/config/test/config.perfect.yaml
@@ -75,8 +75,8 @@ industry:
 
 solving:
   solver:
-    name: highs
-    options: highs-default
+    name: glpk
+    options: glpk-default
   mem: 4000
 
 plotting:
diff --git a/doc/release_notes.rst b/doc/release_notes.rst
index 55e0ad97..6fa88738 100644
--- a/doc/release_notes.rst
+++ b/doc/release_notes.rst
@@ -64,8 +64,6 @@ Upcoming Release
 
 * The ``highs`` solver was added to the default environment file.
 
-* The default solver for testing the workflow in the CI has been changed from ``glpk`` to ``highs``.
-
 
 
 PyPSA-Eur 0.9.0 (5th January 2024)
diff --git a/envs/environment.yaml b/envs/environment.yaml
index 235d7729..26e18f0d 100644
--- a/envs/environment.yaml
+++ b/envs/environment.yaml
@@ -35,6 +35,7 @@ dependencies:
 - netcdf4
 - networkx
 - scipy
+- glpk
 - shapely>=2.0
 - pyscipopt
 - matplotlib