diff --git a/doc/api/next_api_changes/2018-08-29-AL-sankey.rst b/doc/api/next_api_changes/2018-08-29-AL-sankey.rst
new file mode 100644
index 000000000000..9386d5bde3ed
--- /dev/null
+++ b/doc/api/next_api_changes/2018-08-29-AL-sankey.rst
@@ -0,0 +1,9 @@
+Passing a single string as *labels* to `Sankey.add`
+```````````````````````````````````````````````````
+
+Previously, `Sankey.add` would only accept a single string as the *labels*
+argument if its length is equal to the number of flows, in which case it would
+use one character of the string for each flow.
+
+The behavior has been changed to match the documented one: when a single string
+is passed, it is used to label all the flows.
diff --git a/lib/matplotlib/sankey.py b/lib/matplotlib/sankey.py
index 77964a76882e..aa75a1d0bafa 100644
--- a/lib/matplotlib/sankey.py
+++ b/lib/matplotlib/sankey.py
@@ -10,7 +10,7 @@
 from matplotlib.path import Path
 from matplotlib.patches import PathPatch
 from matplotlib.transforms import Affine2D
-from matplotlib import docstring
+from matplotlib import cbook, docstring
 from matplotlib import rcParams
 
 _log = logging.getLogger(__name__)
@@ -449,11 +449,8 @@ def add(self, patchlabel='', flows=None, orientations=None, labels='',
             "orientations and flows must have the same length.\n"
             "orientations has length %d, but flows has length %d."
             % (len(orientations), n))
-        if labels != '' and getattr(labels, '__iter__', False):
-            # np.iterable() isn't used because it would give True if labels is
-            # a string
-            if len(labels) != n:
-                raise ValueError(
+        if not cbook.is_scalar_or_string(labels) and len(labels) != n:
+            raise ValueError(
                 "If labels is a list, then labels and flows must have the "
                 "same length.\nlabels has length %d, but flows has length %d."
                 % (len(labels), n))