diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 6a9353f45146..358b12ca563d 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -1979,6 +1979,8 @@ def acorr(self, x, **kwargs):
         Parameters
         ----------
         x : array-like
+            Not run through Matplotlib's unit conversion, so this should
+            be a unit-less array.
 
         detrend : callable, default: `.mlab.detrend_none` (no detrending)
             A detrending function applied to *x*.  It must have the
@@ -2056,6 +2058,8 @@ def xcorr(self, x, y, normed=True, detrend=mlab.detrend_none,
         Parameters
         ----------
         x, y : array-like of length n
+            Neither *x* nor *y* are run through Matplotlib's unit conversion, so
+            these should be unit-less arrays.
 
         detrend : callable, default: `.mlab.detrend_none` (no detrending)
             A detrending function applied to *x* and *y*.  It must have the
diff --git a/lib/matplotlib/tests/test_datetime.py b/lib/matplotlib/tests/test_datetime.py
index fc1c5f5fbd98..244ee2af2a58 100644
--- a/lib/matplotlib/tests/test_datetime.py
+++ b/lib/matplotlib/tests/test_datetime.py
@@ -8,12 +8,6 @@
 
 
 class TestDatetimePlotting:
-    @pytest.mark.xfail(reason="Test for acorr not written yet")
-    @mpl.style.context("default")
-    def test_acorr(self):
-        fig, ax = plt.subplots()
-        ax.acorr(...)
-
     @mpl.style.context("default")
     def test_annotate(self):
         mpl.rcParams["date.converter"] = 'concise'
@@ -738,9 +732,3 @@ def test_violinplot(self):
     def test_vlines(self):
         fig, ax = plt.subplots()
         ax.vlines(...)
-
-    @pytest.mark.xfail(reason="Test for xcorr not written yet")
-    @mpl.style.context("default")
-    def test_xcorr(self):
-        fig, ax = plt.subplots()
-        ax.xcorr(...)