diff --git a/pde/tools/misc.py b/pde/tools/misc.py
index 1dbf8e7b..d8a988ce 100644
--- a/pde/tools/misc.py
+++ b/pde/tools/misc.py
@@ -389,15 +389,15 @@ def number_array(
         # dtype needs to be determined automatically
         try:
             # convert the result to a numpy array with the given dtype
-            result = np.array(data, dtype=get_common_dtype(data), copy=copy)
+            result = np.array(data, dtype=get_common_dtype(data), copy=copy)  # type: ignore
         except TypeError:
             # Conversion can fail when `data` contains a complex sympy number, i.e.,
             # sympy.I. In this case, we simply try to convert the expression using a
             # complex dtype
-            result = np.array(data, dtype=np.cdouble, copy=copy)
+            result = np.array(data, dtype=np.cdouble, copy=copy)  # type: ignore
 
     else:
         # a specific dtype is requested
-        result = np.array(data, dtype=np.dtype(dtype), copy=copy)
+        result = np.array(data, dtype=np.dtype(dtype), copy=copy)  # type: ignore
 
     return result