diff --git a/skimage/io/tests/test_mpl_imshow.py b/skimage/io/tests/test_mpl_imshow.py
index 0ba75752..7a96607e 100644
--- a/skimage/io/tests/test_mpl_imshow.py
+++ b/skimage/io/tests/test_mpl_imshow.py
@@ -43,7 +43,7 @@ def n_subplots(ax_im):
 
 def test_uint8():
     plt.figure()
-    with expected_warnings(["tight_layout : Falling back to Agg|\A\Z",
+    with expected_warnings(["tight_layout : falling back to Agg|\A\Z",
                             "CObject type is marked|\A\Z"]):
         ax_im = io.imshow(im8)
     assert ax_im.cmap.name == 'gray'
@@ -54,7 +54,7 @@ def test_uint8():
 
 def test_uint16():
     plt.figure()
-    with expected_warnings(["tight_layout : Falling back to Agg|\A\Z",
+    with expected_warnings(["tight_layout : falling back to Agg|\A\Z",
                             "CObject type is marked|\A\Z"]):
         ax_im = io.imshow(im16)
     assert ax_im.cmap.name == 'gray'
@@ -65,7 +65,7 @@ def test_uint16():
 
 def test_float():
     plt.figure()
-    with expected_warnings(["tight_layout : Falling back to Agg|\A\Z",
+    with expected_warnings(["tight_layout : falling back to Agg|\A\Z",
                             "CObject type is marked|\A\Z"]):
         ax_im = io.imshow(imf)
     assert ax_im.cmap.name == 'gray'
@@ -76,7 +76,7 @@ def test_float():
 
 def test_low_dynamic_range():
     with expected_warnings(["Low image dynamic range|CObject type is marked",
-                            "tight_layout : Falling back to Agg|\A\Z"]):
+                            "tight_layout : falling back to Agg|\A\Z"]):
         ax_im = io.imshow(im_lo)
     assert ax_im.get_clim() == (im_lo.min(), im_lo.max())
     # check that a colorbar was created
@@ -90,7 +90,7 @@ def test_outside_standard_range():
     #  Please use capsule objects instead."
     # Ref: https://docs.python.org/2/c-api/cobject.html
     with expected_warnings(["out of standard range|CObject type is marked",
-                            "tight_layout : Falling back to Agg|\A\Z"]):
+                            "tight_layout : falling back to Agg|\A\Z"]):
         ax_im = io.imshow(im_hi)
     assert ax_im.get_clim() == (im_hi.min(), im_hi.max())
     assert n_subplots(ax_im) == 2
@@ -104,7 +104,7 @@ def test_nonstandard_type():
     #  Please use capsule objects instead."
     # Ref: https://docs.python.org/2/c-api/cobject.html
     with expected_warnings(["Low image dynamic range|CObject type is marked",
-                            "tight_layout : Falling back to Agg|\A\Z"]):
+                            "tight_layout : falling back to Agg|\A\Z"]):
         ax_im = io.imshow(im64)
     assert ax_im.get_clim() == (im64.min(), im64.max())
     assert n_subplots(ax_im) == 2
@@ -115,7 +115,7 @@ def test_signed_image():
     plt.figure()
     im_signed = np.array([[-0.5, -0.2], [0.1, 0.4]])
 
-    with expected_warnings(["tight_layout : Falling back to Agg|\A\Z",
+    with expected_warnings(["tight_layout : falling back to Agg|\A\Z",
                             "CObject type is marked|\A\Z"]):
         ax_im = io.imshow(im_signed)
     assert ax_im.get_clim() == (-0.5, 0.5)