@@ -2158,7 +2158,8 @@ def __init__(self):
 
         p.sqrt <<= Group(
             Suppress(Literal(r"\sqrt"))
-            - ((Optional(p.lbracket + p.int_literal + p.rbracket, default=None)
+            - ((Group(Optional(
+                p.lbracket + OneOrMore(~p.rbracket + p.token) + p.rbracket))
                 + p.required_group)
                | Error("Expected \\sqrt{value}"))
         )
@@ -2864,10 +2865,10 @@ def sqrt(self, s, loc, toks):
 
         # Add the root and shift it upward so it is above the tick.
         # The value of 0.6 is a hard-coded hack ;)
-        if root is None:
+        if not root:
             root = Box(check.width * 0.5, 0., 0.)
         else:
-            root = Hlist([Char(x, state) for x in root])
+            root = Hlist(root)
             root.shrink()
             root.shrink()
 
 
@@ -181,7 +181,7 @@ def __call__(self, orig, dest):
                 # just be reported as a regular exception below).
                 "DISPLAY": "",
                 # Do not load any user options.
-                "INKSCAPE_PROFILE_DIR": os.devnull,
+                "INKSCAPE_PROFILE_DIR": self._tmpdir.name,
             }
             # Old versions of Inkscape (e.g. 0.48.3.1) seem to sometimes
             # deadlock when stderr is redirected to a pipe, so we redirect it
@@ -233,6 +233,15 @@ def __del__(self):
             self._tmpdir.cleanup()
 
 
+class _SVGWithMatplotlibFontsConverter(_SVGConverter):
+    def __call__(self, orig, dest):
+        if not hasattr(self, "_tmpdir"):
+            self._tmpdir = TemporaryDirectory()
+            shutil.copytree(cbook._get_data_path("fonts/ttf"),
+                            Path(self._tmpdir.name, "fonts"))
+        return super().__call__(orig, dest)
+
+
 def _update_converter():
     try:
         mpl._get_executable_info("gs")
@@ -254,6 +263,7 @@ def _update_converter():
 #: extension to png format.
 converter = {}
 _update_converter()
+_svg_with_matplotlib_fonts_converter = _SVGWithMatplotlibFontsConverter()
 
 
 def comparable_formats():
@@ -303,7 +313,12 @@ def convert(filename, cache):
                 return str(newpath)
 
         _log.debug("For %s: converting to png.", filename)
-        converter[path.suffix[1:]](path, newpath)
+        convert = converter[path.suffix[1:]]
+        if path.suffix == ".svg":
+            contents = path.read_text()
+            if 'style="font:' in contents:  # for svg.fonttype = none.
+                convert = _svg_with_matplotlib_fonts_converter
+        convert(path, newpath)
 
         if cache_dir is not None:
             _log.debug("For %s: caching conversion result.", filename)
 
@@ -112,6 +112,9 @@
     r'$\left(X\right)_{a}^{b}$',  # github issue 7615
     r'$\dfrac{\$100.00}{y}$',  # github issue #1888
 ]
+svg_only_math_tests = [
+    r'$\sqrt[ab]{123}$',  # github issue #8665
+]
 
 digits = "0123456789"
 uppercase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
@@ -167,8 +170,6 @@
         for set in chars:
             font_tests.append(wrapper % set)
 
-font_tests = list(filter(lambda x: x[1] is not None, enumerate(font_tests)))
-
 
 @pytest.fixture
 def baseline_images(request, fontset, index):
@@ -192,6 +193,32 @@ def test_mathtext_rendering(baseline_images, fontset, index, test):
              horizontalalignment='center', verticalalignment='center')
 
 
+cur_svg_only_math_tests = list(
+    filter(lambda x: x[1] is not None, enumerate(svg_only_math_tests)))
+
+
+@pytest.mark.parametrize('index, test', cur_svg_only_math_tests,
+                         ids=[str(idx) for idx, _ in cur_svg_only_math_tests])
+@pytest.mark.parametrize('fontset', ['all'])
+@pytest.mark.parametrize('baseline_images', ['mathtext1'], indirect=True)
+@image_comparison(
+    baseline_images=None, extensions=['svg'],
+    savefig_kwarg={
+        'metadata': {  # Minimize svg size.
+            'Creator': None, 'Date': None, 'Format': None, 'Type': None}})
+def test_mathtext_rendering_svg_only(baseline_images, fontset, index, test):
+    mpl.rcParams['svg.fonttype'] = 'none'
+    fig = plt.figure(figsize=(5.25, 5.25))
+    fig.patch.set_visible(False)  # Minimize svg size.
+    fontsets = ['cm', 'stix', 'stixsans', 'dejavusans', 'dejavuserif']
+    for i, fontset in enumerate(fontsets):
+        fig.text(0.5, (i + .5) / len(fontsets), test, math_fontfamily=fontset,
+                 horizontalalignment='center', verticalalignment='center')
+
+
+font_tests = list(filter(lambda x: x[1] is not None, enumerate(font_tests)))
+
+
 @pytest.mark.parametrize('index, test', font_tests,
                          ids=[str(index) for index, _ in font_tests])
 @pytest.mark.parametrize('fontset',