diff --git a/src/pydocstyle/checker.py b/src/pydocstyle/checker.py
index d75e6827..29cbff9d 100644
--- a/src/pydocstyle/checker.py
+++ b/src/pydocstyle/checker.py
@@ -46,20 +46,12 @@ def decorator(f):
     return decorator
 
 
-FSTRING_RE = re(r'^[rR]?[fF]')
+_FSTRING_REGEX = re(r'^[rR]?[fF]')
 
 
-def is_fstring(docstring):
-    r"""Return True if docstring is an f-string.
-
-    >>> is_fstring('rf"abc"')
-    True
-    >>> is_fstring('F"abc"')
-    True
-    >>> is_fstring("u'''abc'''")
-    False
-    """
-    return FSTRING_RE.match(str(docstring))
+def _is_fstring(docstring):
+    """Return True if docstring is an f-string."""
+    return _FSTRING_REGEX.match(str(docstring))
 
 
 class ConventionChecker:
@@ -204,7 +196,7 @@ def check_docstring_fstring(self, definition, docstring):
         and users may attempt to use them as docstrings. This is an
         outright mistake so we issue a specific error code.
         """
-        if is_fstring(docstring):
+        if _is_fstring(docstring):
             return violations.D303()
 
     @check_for(Definition, terminal=True)
@@ -221,7 +213,7 @@ def check_docstring_missing(self, definition, docstring):
               with a single underscore.
 
         """
-        if is_fstring(docstring):
+        if _is_fstring(docstring):
             return  # checked above in check_docstring_fstring
 
         if (
diff --git a/src/pydocstyle/violations.py b/src/pydocstyle/violations.py
index 870095f0..a5bf5c1e 100644
--- a/src/pydocstyle/violations.py
+++ b/src/pydocstyle/violations.py
@@ -312,7 +312,10 @@ def to_rst(cls) -> str:
     'D302',
     'Deprecated: Use u""" for Unicode docstrings',
 )
-D303 = D3xx.create_error('D303', 'f-strings are not valid as docstrings')
+D303 = D3xx.create_error(
+    'D303',
+    'f-strings are not valid as docstrings',
+)
 
 D4xx = ErrorRegistry.create_group('D4', 'Docstring Content Issues')
 D400 = D4xx.create_error(
diff --git a/src/tests/test_cases/fstrings.py b/src/tests/test_cases/fstrings.py
new file mode 100644
index 00000000..ee8756ca
--- /dev/null
+++ b/src/tests/test_cases/fstrings.py
@@ -0,0 +1,47 @@
+"""Test for warning about f-strings as docstrings."""
+
+from .expected import Expectation
+
+expectation = Expectation()
+expect = expectation.expect
+_GIZMO = "gizmo"
+D303 = expect("D303: f-strings are not valid as docstrings")
+
+
+@D303
+def fstring():
+    f"""Toggle the gizmo."""
+
+
+@D303
+def another_fstring():
+    F"""Toggle the gizmo."""
+
+
+@D303
+def fstring_with_raw():
+    rF"""Toggle the gizmo."""
+
+
+@D303
+def fstring_with_raw_caps():
+    RF"""Toggle the gizmo."""
+
+
+@D303
+def fstring_with_raw_variable():
+    RF"""Toggle the {_GIZMO}."""
+
+
+@D303
+def fstring_with_variable():
+    f"""Toggle the {_GIZMO.upper()}."""
+
+
+@D303
+def fstring_with_other_errors(arg=1, missing_arg=2):
+    f"""Toggle the {_GIZMO.upper()}
+
+    This should not raise any other errors since fstrings
+    are a terminal check.
+    """
diff --git a/src/tests/test_definitions.py b/src/tests/test_definitions.py
index 3971f0a0..605d9bb9 100644
--- a/src/tests/test_definitions.py
+++ b/src/tests/test_definitions.py
@@ -20,6 +20,7 @@
     'noqa',
     'sections',
     'functions',
+    'fstrings',
     'canonical_google_examples',
     'canonical_numpy_examples',
     'canonical_pep257_examples',