diff --git a/artistools/inputmodel/plotinitialcomposition.py b/artistools/inputmodel/plotinitialcomposition.py
index beb5a3bf2..6032aadc1 100755
--- a/artistools/inputmodel/plotinitialcomposition.py
+++ b/artistools/inputmodel/plotinitialcomposition.py
@@ -9,9 +9,9 @@
 from pathlib import Path
 
 import argcomplete
+import matplotlib.cm as mplcm
+import matplotlib.colors as mplcolors
 import matplotlib.pyplot as plt
-import matplotlibcm as mplcm
-import matplotlibcolors as mplcolors
 import numpy as np
 import pandas as pd
 from astropy import units as u
diff --git a/artistools/lightcurve/plotlightcurve.py b/artistools/lightcurve/plotlightcurve.py
index 869d954ea..bc060f758 100644
--- a/artistools/lightcurve/plotlightcurve.py
+++ b/artistools/lightcurve/plotlightcurve.py
@@ -385,7 +385,7 @@ def plot_artis_lightcurve(
         )
         nts_last, validrange_start_days, validrange_end_days = None, -math.inf, math.inf
 
-    colorindex = None
+    colorindex: t.Any = None
     for dirbin in dirbins:
         lcdata = lcdataframes[dirbin]
 
diff --git a/artistools/lightcurve/viewingangleanalysis.py b/artistools/lightcurve/viewingangleanalysis.py
index 923eeaf52..c6e9b6c00 100644
--- a/artistools/lightcurve/viewingangleanalysis.py
+++ b/artistools/lightcurve/viewingangleanalysis.py
@@ -456,6 +456,7 @@ def update_plotkwargs_for_viewingangle_colorbar(
     angles = np.arange(0, at.get_viewingdirectionbincount())
     colors = []
     for angle in angles:
+        colorindex: t.Any
         _, colorindex = at.lightcurve.plotlightcurve.get_viewinganglecolor_for_colorbar(
             angle,
             costheta_viewing_angle_bins,
@@ -630,7 +631,9 @@ def make_peak_colour_viewing_angle_plot(args):
             print(f"All 100 angles are not in file {datafilename}. Quitting")
             sys.exit(1)
 
-        second_band_brightness = second_band_brightness_at_peak_first_band(data, bands, modelpath, modelnumber, args)
+        second_band_brightness: t.Any = second_band_brightness_at_peak_first_band(
+            data, bands, modelpath, modelnumber, args
+        )
 
         data[f"{bands[1]}at{bands[0]}max"] = second_band_brightness
 
@@ -725,6 +728,7 @@ def peakmag_risetime_declinerate_init(modelpaths, filternames_conversion_dict, a
             modelname = at.get_model_name(modelpath)
             modelnames.append(modelname)  # save for later
             print(f"Reading spectra: {modelname}")
+            lightcurve_data: t.Any
             if args.filter:
                 lightcurve_data = at.lightcurve.generate_band_lightcurve_data(
                     modelpath, args, angle, modelnumber=modelnumber
@@ -794,7 +798,7 @@ def plot_viewanglebrightness_at_fixed_time(modelpath, args):
 
     plotkwargs = {}
 
-    lcdataframes = at.lightcurve.readfile(modelpath / "light_curve_res.out")
+    lcdataframes: t.Any = at.lightcurve.readfile(modelpath / "light_curve_res.out")
 
     timetoplot = at.match_closest_time(reftime=args.timedays, searchtimes=lcdataframes[0]["time"])
     print(timetoplot)
diff --git a/artistools/plottools.py b/artistools/plottools.py
index 3b26c2448..187e23aa4 100644
--- a/artistools/plottools.py
+++ b/artistools/plottools.py
@@ -28,6 +28,7 @@ def _set_formatted_label_text(self):
         if stroffset:
             stroffset = stroffset.replace(r"$\times", "$") + " "
         strnewlabel = self.labeltemplate.format(stroffset)
+        assert self.axis is not None
         self.axis.set_label_text(strnewlabel)
         assert self.offset == 0
         self.axis.offsetText.set_visible(False)
@@ -178,7 +179,7 @@ def autoscale(ax=None, axis="y", margin=0.1):
     From https://stackoverflow.com/questions/29461608/matplotlib-fixing-x-axis-scale-and-autoscale-y-axis
     """
 
-    def calculate_new_limit(fixed, dependent, limit):
+    def calculate_new_limit(fixed, dependent, limit) -> tuple[float, float]:
         """Calculate the min/max of the dependent axis given a fixed axis with limits."""
         if len(fixed) > 2:
             mask = (fixed > limit[0]) & (fixed < limit[1]) & (~np.isnan(dependent)) & (~np.isnan(fixed))
@@ -211,7 +212,7 @@ def get_xy(artist):
         ax = plt.gca()
     newlow, newhigh = np.inf, -np.inf
 
-    for artist in ax.collections + ax.lines:
+    for artist in list(ax.collections) + list(ax.lines):
         x, y = get_xy(artist)
         if axis == "y":
             setlim = ax.set_ylim
diff --git a/artistools/radfield.py b/artistools/radfield.py
index 37cdff581..d4e0cdb9a 100755
--- a/artistools/radfield.py
+++ b/artistools/radfield.py
@@ -65,6 +65,7 @@ def select_bin(radfielddata, nu=None, lambda_angstroms=None, modelgridindex=None
     if lambda_angstroms is not None:
         nu = 2.99792458e18 / lambda_angstroms
     else:
+        assert nu is not None
         lambda_angstroms = 2.99792458e18 / nu
 
     dfselected = radfielddata.query(
diff --git a/artistools/spectra/plotspectra.py b/artistools/spectra/plotspectra.py
index 5a733c442..bc30c6f3f 100755
--- a/artistools/spectra/plotspectra.py
+++ b/artistools/spectra/plotspectra.py
@@ -9,7 +9,7 @@
 from pathlib import Path
 
 import argcomplete
-import matplotlib.artis as mplartist
+import matplotlib.artist as mplartist
 import matplotlib.axes as mplax
 import matplotlib.figure as mplfig
 import matplotlib.patches as mpatches
diff --git a/pyproject.toml b/pyproject.toml
index c9996562a..13e2b244e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -141,7 +141,7 @@ disallow_incomplete_defs = true
 disallow_untyped_calls = true
 disallow_untyped_defs = true
 enable_error_code = [
-  #"possibly-undefined",
+  "possibly-undefined",
 ]
  
 [[tool.mypy.overrides]]