diff --git a/zipline/lib/rank.pyx b/zipline/lib/rank.pyx
index a23fa231..022b39b8 100644
--- a/zipline/lib/rank.pyx
+++ b/zipline/lib/rank.pyx
@@ -18,7 +18,7 @@ from numpy import apply_along_axis, float64, isnan, nan
 from scipy.stats import rankdata
 
 from zipline.utils.numpy_utils import (
-    is_float,
+    is_missing,
     float64_dtype,
     int64_dtype,
     datetime64ns_dtype,
@@ -28,15 +28,6 @@ from zipline.utils.numpy_utils import (
 import_array()
 
 
-cpdef is_missing(ndarray data, object missing_value):
-    """
-    Generic is_missing function that handles quirks with NaN.
-    """
-    if is_float(data) and isnan(missing_value):
-        return isnan(data)
-    return (data == missing_value)
-
-
 def rankdata_1d_descending(ndarray data, str method):
     """
     1D descending version of scipy.stats.rankdata.
diff --git a/zipline/testing/core.py b/zipline/testing/core.py
index 3517a2e3..f9832767 100644
--- a/zipline/testing/core.py
+++ b/zipline/testing/core.py
@@ -49,7 +49,7 @@ from zipline.pipeline.loaders.testing import make_seeded_random_loader
 from zipline.utils import security_list
 from zipline.utils.calendars import get_calendar
 from zipline.utils.input_validation import expect_dimensions
-from zipline.utils.numpy_utils import as_column
+from zipline.utils.numpy_utils import as_column, isnat
 from zipline.utils.pandas_utils import timedelta_to_integral_seconds
 from zipline.utils.sentinel import sentinel
 
@@ -394,6 +394,18 @@ def check_arrays(x, y, err_msg='', verbose=True, check_dtypes=True):
         # ...then check the actual values as well.
         x = x.as_string_array()
         y = y.as_string_array()
+    elif x.dtype.kind in 'mM':
+        x_isnat = isnat(x)
+        y_isnat = isnat(y)
+        assert_array_equal(
+            x_isnat,
+            y_isnat,
+            err_msg="NaTs not equal",
+            verbose=verbose,
+        )
+        # Fill NaTs with zero for comparison.
+        x = np.where(x_isnat, np.zeros_like(x), x)
+        y = np.where(x_isnat, np.zeros_like(x), x)
 
     return assert_array_equal(x, y, err_msg=err_msg, verbose=verbose)
 
diff --git a/zipline/utils/numpy_utils.py b/zipline/utils/numpy_utils.py
index e8e2be52..77371da6 100644
--- a/zipline/utils/numpy_utils.py
+++ b/zipline/utils/numpy_utils.py
@@ -17,8 +17,8 @@ from numpy import (
     empty,
     flatnonzero,
     hstack,
+    isnan,
     nan,
-    timedelta64,
     vectorize,
     where
 )
@@ -287,6 +287,28 @@ def rolling_window(array, length):
 
 # Sentinel value that isn't NaT.
 _notNaT = make_datetime64D(0)
+iNaT = NaTns.view(int64_dtype)
+assert iNaT == NaTD.view(int64_dtype), "iNaTns != iNaTD"
+
+
+def isnat(obj):
+    """
+    Check if a value is np.NaT.
+    """
+    if obj.dtype.kind not in ('m', 'M'):
+        raise ValueError("%s is not a numpy datetime or timedelta")
+    return obj.view(int64_dtype) == iNaT
+
+
+def is_missing(data, missing_value):
+    """
+    Generic is_missing function that handles NaN and NaT.
+    """
+    if is_float(data) and isnan(missing_value):
+        return isnan(data)
+    elif is_datetime(data) and isnat(missing_value):
+        return isnat(data)
+    return (data == missing_value)
 
 
 def busday_count_mask_NaT(begindates, enddates, out=None):
@@ -304,8 +326,8 @@ def busday_count_mask_NaT(begindates, enddates, out=None):
     if out is None:
         out = empty(broadcast(begindates, enddates).shape, dtype=float)
 
-    beginmask = (begindates == NaTD)
-    endmask = (enddates == NaTD)
+    beginmask = isnat(begindates)
+    endmask = isnat(enddates)
 
     out = busday_count(
         # Temporarily fill in non-NaT values.