diff --git a/requirements_sles15.txt b/requirements_sles15.txt
index 52dfb8e6..39ce5a93 100644
--- a/requirements_sles15.txt
+++ b/requirements_sles15.txt
@@ -1,20 +1,20 @@
 setuptools>=59.4.0
 pyyaml>=6.0
-pycodestyle>=2.8.0
+pycodestyle>=2.11.0
 netCDF4
 matplotlib
 cartopy>=0.21.1
 scipy>=1.9.3
 xarray>=2022.3.0
 pandas>=1.4.0
-numpy==1.22.3
-attrs==21.4.0
+numpy<2
+attrs
 
 # Not explicitly part of eva but dependcies of eva dependencies already in spack-stack
 # versions need to be set to avoid other versions being picked
 pyproj
 importlib_metadata==7.1.0
-contourpy==1.0.7
+contourpy
 msgpack>=1.0.0
 
 # Additional packages
diff --git a/src/eva/transforms/arithmetic.py b/src/eva/transforms/arithmetic.py
index 569a1664..fe13e172 100644
--- a/src/eva/transforms/arithmetic.py
+++ b/src/eva/transforms/arithmetic.py
@@ -140,7 +140,7 @@ def arithmetic(config, data_collections):
                 regex_string = r'\(|\)|-|\*|\+|\/|,'
                 # add defined functions the user may apply
                 for fname in defined_functions:
-                    regex_string += '|{}'.format(fname)
+                    regex_string += r'|\b{}\b'.format(re.escape(fname))
                 expression_elements = re.split(regex_string, expression)
 
                 # Remove empty elements and duplicates from expression elements