diff --git a/devtools/conda-envs/test_env.yaml b/devtools/conda-envs/test_env.yaml
index 831b4dbd..ac8b28e6 100644
--- a/devtools/conda-envs/test_env.yaml
+++ b/devtools/conda-envs/test_env.yaml
@@ -16,7 +16,7 @@ dependencies:
   - codecov
 
     # Package dependencies
-  - numpy
+  - numpy<2
   - pandas
   - pytorch
   - pydantic<2
diff --git a/mlcolvar/utils/fes.py b/mlcolvar/utils/fes.py
index 4bf34c8d..a5961fd4 100644
--- a/mlcolvar/utils/fes.py
+++ b/mlcolvar/utils/fes.py
@@ -180,7 +180,7 @@ def compute_fes(
                 (X[:, i].min() - offset, X[:, i].max() + offset) for i in range(dim)
             ]
         grid_list = [np.linspace(b[0], b[1], num_samples) for b in bounds]
-        grid = np.meshgrid(*grid_list)
+        grid = list(np.meshgrid(*grid_list))
         positions = np.vstack([g.ravel() for g in grid]).T
 
     # divide in blocks
diff --git a/requirements.txt b/requirements.txt
index 32acba71..c5283ab0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 lightning
 torch
-numpy
+numpy<2
 pandas
 matplotlib
 kdepy
\ No newline at end of file