diff --git a/obsarray/templater/dataset_util.py b/obsarray/templater/dataset_util.py
index c1fbe57..4e0fc11 100644
--- a/obsarray/templater/dataset_util.py
+++ b/obsarray/templater/dataset_util.py
@@ -454,15 +454,15 @@ def get_default_fill_value(dtype: numpy.typecodes) -> Union[int, float]:
         if dtype == numpy.int8:
             return numpy.int8(-127)
         if dtype == numpy.uint8:
-            return numpy.uint8(-1)
+            return numpy.iinfo(numpy.uint8).max
         elif dtype == numpy.int16:
             return numpy.int16(-32767)
         elif dtype == numpy.uint16:
-            return numpy.uint16(-1)
+            return numpy.iinfo(numpy.uint16).max
         elif dtype == numpy.int32:
             return numpy.int32(-2147483647)
         elif dtype == numpy.uint32:
-            return numpy.uint32(-1)
+            return numpy.iinfo(numpy.uint32).max
         elif dtype == numpy.int64:
             return numpy.int64(-9223372036854775806)
         elif dtype == numpy.float32:
diff --git a/setup.py b/setup.py
index 1755ebd..b41a6fa 100644
--- a/setup.py
+++ b/setup.py
@@ -25,7 +25,7 @@ def read(filename):
     description="Measurement data handling in Python",
     long_description=read("README.md"),
     packages=find_packages(exclude=("tests",)),
-    install_requires=["comet_maths", "netcdf4==1.6.5", "xarray"],
+    install_requires=["comet_maths", "netcdf4", "xarray"],
     extras_require={
         "dev": [
             "pre-commit",