diff --git a/CHANGES.rst b/CHANGES.rst
index 177e83dd..f273fddf 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -24,6 +24,7 @@ Adds:
 
 Fixes:
 
+- add note on string not containing uncertainty to `ufloat_fromstr` doctring (#287)
 - fix typos in `ufloat_fromstr` docstring examples (#285)
 - fix `readthedocs` configuration so that the build passes (#254)
 - adjust `codecov.io` configuration so that minor code coverage changes will not result
diff --git a/uncertainties/core.py b/uncertainties/core.py
index 10771703..cf66809a 100644
--- a/uncertainties/core.py
+++ b/uncertainties/core.py
@@ -985,6 +985,11 @@ def ufloat_fromstr(representation, tag=None):
        That is, "1.25(3)" is the same as `ufloat(1.25, 0.03)`,
        while "1.25(3.)" is the same as `ufloat(1.25, 3.)`
 
+    3. If the representation does not contain an uncertainty, an
+       uncertainty of 1 in the least significant digit is assigned to
+       the nominal value. For nominal values corresponding to "nan", an
+       uncertainty of 1 is assigned.
+
     Examples:
     -----------
 
@@ -998,6 +1003,7 @@ def ufloat_fromstr(representation, tag=None):
     >>> x = ufloat_fromstr("680(41)e-3")  # = ufloat(0.68, 0.041)
     >>> x = ufloat_fromstr("23.2")  # = ufloat(23.2, 0.1)
     >>> x = ufloat_fromstr("23.29")  # = ufloat(23.29, 0.01)
+    >>> x = ufloat_fromstr("nan")  # = ufloat(numpy.nan, 1.0)
 
     >>> x = ufloat_fromstr("680.3(nan)") # = ufloat(680.3, numpy.nan)
     """