diff --git a/HISTORY.rst b/HISTORY.rst
index dfa5a1e..6cebed4 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -1,6 +1,9 @@
 =======
 History
 =======
+2024.8.22 -- Bugfix: error in number of cores.
+   * Fixed an error if options for number of cores were strings, not numbers.
+     
 2024.7.31 -- Bugfix and improvements for parallel runs
    * There was an issue saving the pressure and volume as properties due to a mismatch
      in the names used. This has been corrected.
diff --git a/lammps_step/lammps.py b/lammps_step/lammps.py
index b240a4a..0c42da9 100644
--- a/lammps_step/lammps.py
+++ b/lammps_step/lammps.py
@@ -405,9 +405,9 @@ def run(self):
         if global_options["parallelism"] in ("any", "mpi"):
             np = n_atoms // o["atoms_per_core"] + 1
             if o["ncores"] != "available":
-                np = min(np, o["ncores"])
+                np = min(np, int(o["ncores"]))
             if global_options["ncores"] != "available":
-                np = min(np, global_options["ncores"])
+                np = min(np, int(global_options["ncores"]))
         else:
             np = 1