diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index dc7b82386216..f137d15e226f 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -725,6 +725,7 @@ def axhline(self, y=0, xmin=0, xmax=1, **kwargs):
         trans = self.get_yaxis_transform(which='grid')
         l = mlines.Line2D([xmin, xmax], [y, y], transform=trans, **kwargs)
         self.add_line(l)
+        self.ignore_existing_data_limits = True
         self.autoscale_view(scalex=False, scaley=scaley)
         return l
 
@@ -791,6 +792,7 @@ def axvline(self, x=0, ymin=0, ymax=1, **kwargs):
         trans = self.get_xaxis_transform(which='grid')
         l = mlines.Line2D([x, x], [ymin, ymax], transform=trans, **kwargs)
         self.add_line(l)
+        self.ignore_existing_data_limits = True
         self.autoscale_view(scalex=scalex, scaley=False)
         return l
 
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
index dcebf02af1be..0115cfcd151e 100644
--- a/lib/matplotlib/tests/test_axes.py
+++ b/lib/matplotlib/tests/test_axes.py
@@ -4974,6 +4974,41 @@ def test_bar_single_height():
     ax.bar(0, 1, bottom=range(4), width=1, orientation='horizontal')
 
 
+def test_datetime_axhline_same_axes():
+    # This test was suggested by Paul Hobson (@phobson) regarding issue 7742
+    # Check when ploting datetime data and horizontal line
+    # order of plotting doesn't matter.
+    # axhline() should not change x axis limits.
+    from datetime import datetime
+    fig, axs = plt.subplots(2, 1)
+    xvalues = [datetime(2016, 1, 1, 0, 0, 0), datetime(2016, 1, 2, 0, 0, 0)]
+    yvalues = [1, 2]
+
+    axs[0].plot(xvalues, yvalues)
+    axs[0].axhline(1.5)
+
+    axs[1].axhline(1.5)
+    axs[1].plot(xvalues, yvalues)
+
+    assert (axs[0].get_xlim() == axs[1].get_xlim())
+
+
+def test_datetime_axvline_same_axes():
+    # This is similar to test above
+    from datetime import datetime
+    fig, axs = plt.subplots(2, 1)
+    xvalues = [1, 2]
+    yvalues = [datetime(2016, 1, 1, 0, 0, 0), datetime(2016, 1, 2, 0, 0, 0)]
+
+    axs[0].plot(xvalues, yvalues)
+    axs[0].axvline(1.5)
+
+    axs[1].axvline(1.5)
+    axs[1].plot(xvalues, yvalues)
+
+    assert (axs[0].get_ylim() == axs[1].get_ylim())
+
+
 def test_invalid_axis_limits():
     plt.plot([0, 1], [0, 1])
     with pytest.raises(ValueError):