diff --git a/pandas/_libs/src/util.pxd b/pandas/_libs/src/util.pxd
index d8249ec130f4d..2c1876fad95d2 100644
--- a/pandas/_libs/src/util.pxd
+++ b/pandas/_libs/src/util.pxd
@@ -161,3 +161,18 @@ cdef inline bint _checknull(object val):
 
 cdef inline bint is_period_object(object val):
     return getattr(val, '_typ', '_typ') == 'period'
+
+
+cdef inline bint is_offset_object(object val):
+    """
+    Check if an object is a DateOffset object.
+
+    Parameters
+    ----------
+    val : object
+
+    Returns
+    -------
+    is_date_offset : bool
+    """
+    return getattr(val, '_typ', None) == "dateoffset"
diff --git a/pandas/_libs/tslib.pyx b/pandas/_libs/tslib.pyx
index 4f73f196b0d9d..6588b5476e2b9 100644
--- a/pandas/_libs/tslib.pyx
+++ b/pandas/_libs/tslib.pyx
@@ -125,7 +125,7 @@ def ints_to_pydatetime(ndarray[int64_t] arr, tz=None, freq=None,
     elif box == "datetime":
         func_create = create_datetime_from_ts
     else:
-        raise ValueError("box must be one of 'datetime', 'date', 'time' or" +
+        raise ValueError("box must be one of 'datetime', 'date', 'time' or"
                          " 'timestamp'")
 
     if tz is not None:
diff --git a/pandas/_libs/tslibs/period.pyx b/pandas/_libs/tslibs/period.pyx
index 008747c0a9e78..cc2fb6e0617cb 100644
--- a/pandas/_libs/tslibs/period.pyx
+++ b/pandas/_libs/tslibs/period.pyx
@@ -19,7 +19,8 @@ from pandas.compat import PY2
 
 cimport cython
 
-from cpython.datetime cimport PyDateTime_Check, PyDateTime_IMPORT
+from cpython.datetime cimport (PyDateTime_Check, PyDelta_Check,
+                               PyDateTime_IMPORT)
 # import datetime C API
 PyDateTime_IMPORT
 
@@ -1058,18 +1059,21 @@ cdef class _Period(object):
         return hash((self.ordinal, self.freqstr))
 
     def _add_delta(self, other):
-        if isinstance(other, (timedelta, np.timedelta64, offsets.Tick)):
+        cdef:
+            int64_t nanos, offset_nanos
+
+        if (PyDelta_Check(other) or util.is_timedelta64_object(other) or
+                isinstance(other, offsets.Tick)):
             offset = frequencies.to_offset(self.freq.rule_code)
             if isinstance(offset, offsets.Tick):
                 nanos = delta_to_nanoseconds(other)
                 offset_nanos = delta_to_nanoseconds(offset)
-
                 if nanos % offset_nanos == 0:
                     ordinal = self.ordinal + (nanos // offset_nanos)
                     return Period(ordinal=ordinal, freq=self.freq)
             msg = 'Input cannot be converted to Period(freq={0})'
             raise IncompatibleFrequency(msg.format(self.freqstr))
-        elif isinstance(other, offsets.DateOffset):
+        elif util.is_offset_object(other):
             freqstr = other.rule_code
             base = get_base_alias(freqstr)
             if base == self.freq.rule_code:
@@ -1082,8 +1086,8 @@ cdef class _Period(object):
 
     def __add__(self, other):
         if is_period_object(self):
-            if isinstance(other, (timedelta, np.timedelta64,
-                                  offsets.DateOffset)):
+            if (PyDelta_Check(other) or util.is_timedelta64_object(other) or
+                    util.is_offset_object(other)):
                 return self._add_delta(other)
             elif other is NaT:
                 return NaT
@@ -1109,8 +1113,8 @@ cdef class _Period(object):
 
     def __sub__(self, other):
         if is_period_object(self):
-            if isinstance(other, (timedelta, np.timedelta64,
-                                  offsets.DateOffset)):
+            if (PyDelta_Check(other) or util.is_timedelta64_object(other) or
+                    util.is_offset_object(other)):
                 neg_other = -other
                 return self + neg_other
             elif util.is_integer_object(other):