diff --git a/numpy_groupies/aggregate_numpy.py b/numpy_groupies/aggregate_numpy.py
index 9dd82a8..0299312 100644
--- a/numpy_groupies/aggregate_numpy.py
+++ b/numpy_groupies/aggregate_numpy.py
@@ -272,6 +272,7 @@ def _nancumsum(group_idx, a, size, fill_value=None, dtype=None):
     generic=_generic_callable,
 )
 _impl_dict.update(("nan" + k, v) for k, v in list(_impl_dict.items()) if k not in funcs_no_separate_nan)
+_impl_dict["nancumsum"] = _nancumsum
 
 
 def _aggregate_base(
@@ -308,6 +309,8 @@ def _aggregate_base(
             if "nan" in func:
                 if "arg" in func:
                     kwargs["_nansqueeze"] = True
+                elif "cum" in func:
+                    pass
                 else:
                     good = ~np.isnan(a)
                     if "len" not in func or is_pandas:
diff --git a/numpy_groupies/tests/test_compare.py b/numpy_groupies/tests/test_compare.py
index 4261541..6e45d63 100644
--- a/numpy_groupies/tests/test_compare.py
+++ b/numpy_groupies/tests/test_compare.py
@@ -4,7 +4,6 @@
 may throw NotImplementedError in order to show missing functionality without throwing
 test errors. 
 """
-import sys
 from itertools import product
 
 import numpy as np
diff --git a/numpy_groupies/tests/test_generic.py b/numpy_groupies/tests/test_generic.py
index 9cf99fa..a6eac40 100644
--- a/numpy_groupies/tests/test_generic.py
+++ b/numpy_groupies/tests/test_generic.py
@@ -24,6 +24,12 @@ def _deselect_purepy(aggregate_all, *args, **kwargs):
     return aggregate_all.__name__.endswith("purepy")
 
 
+def _deselect_purepy_and_pandas(aggregate_all, *args, **kwargs):
+    # purepy and pandas implementation handle some nan cases differently.
+    # So they need to be excluded from several tests."""
+    return aggregate_all.__name__.endswith(("pandas", "purepy"))
+
+
 def _deselect_purepy_and_invalid_axis(aggregate_all, size, axis, *args, **kwargs):
     if axis >= len(size):
         return True
@@ -358,6 +364,17 @@ def test_cumsum(aggregate_all):
     np.testing.assert_array_equal(res, ref)
 
 
+@pytest.mark.deselect_if(func=_deselect_purepy_and_pandas)
+def test_nancumsum(aggregate_all):
+    # https://github.com/ml31415/numpy-groupies/issues/79
+    group_idx = [0, 0, 0, 1, 1, 0, 0]
+    a = [2, 2, np.nan, 2, 2, 2, 2]
+    ref = [2., 4., 4., 2., 4., 6., 8.]
+
+    res = aggregate_all(group_idx, a, func="nancumsum")
+    np.testing.assert_array_equal(res, ref)
+
+
 def test_cummax(aggregate_all):
     group_idx = np.array([4, 3, 3, 4, 4, 1, 1, 1, 7, 8, 7, 4, 3, 3, 1, 1])
     a = np.array([3, 4, 1, 3, 9, 9, 6, 7, 7, 0, 8, 2, 1, 8, 9, 8])
diff --git a/numpy_groupies/utils.py b/numpy_groupies/utils.py
index e2af7a3..56befb5 100644
--- a/numpy_groupies/utils.py
+++ b/numpy_groupies/utils.py
@@ -117,6 +117,8 @@
     np.array: "array",
     np.asarray: "array",
     np.sort: "sort",
+    np.cumsum: "cumsum",
+    np.cumprod: "cumprod",
     np.nansum: "nansum",
     np.nanprod: "nanprod",
     np.nanmean: "nanmean",
@@ -126,8 +128,7 @@
     np.nanstd: "nanstd",
     np.nanargmax: "nanargmax",
     np.nanargmin: "nanargmin",
-    np.cumsum: "cumsum",
-    np.cumprod: "cumprod",
+    np.nancumsum: "nancumsum",
 }
 
 
@@ -150,7 +151,7 @@ def get_aliasing(*extra):
     alias.update((k, k) for k in set(alias.values()))
     # Treat nan-functions as firstclass member and add them directly
     for key in set(alias.values()):
-        if key not in funcs_no_separate_nan:
+        if key not in funcs_no_separate_nan and not key.startswith("nan"):
             key = "nan" + key
             alias[key] = key
     return alias