diff --git a/testing/web-platform/tests/fonts/math/radical-negativekernbeforedegree1000-rulethickness1000.woff b/testing/web-platform/tests/fonts/math/radical-negativekernbeforedegree1000-rulethickness1000.woff
new file mode 100644
index 000000000000..ed6ce88c39e2
--- /dev/null
+++ b/testing/web-platform/tests/fonts/math/radical-negativekernbeforedegree1000-rulethickness1000.woff
@@ -0,0 +1,319 @@
+wOFFOTTO
+d
+CFF
+t
+)
+9
+FFTM
+7W
+MATH
+9
+eOS
+/
+2
+\
+2
+cmap
+C
+JD
+(
+head
+.
+6
+9hhea
+8
+=
+hmtx
+T
+maxp
+T
+P
+name
+{
+)
+ypost
+\
+3x
+c
+d
+b
+|
+6_
+_
+E
+n
+L3
+_
+8
+<
+ET
+^
+x
+c
+d
+~
+&
+AlF
+T
+P
+2
+P
+x
+c
+a
+~
+8
+a
+fr
+f4
+0
+AAI
+w
+\
+x
+Mj
+0
+M
+I
+Fv
+P
+V
+[
+Av
+9
+C
+8
+G
+r
+Z
+X
+7
+7
+w
+'
+b
+-
+W
+!
+n
++
+<
+5
+M
+f
+5V
+]
+8
+e
+j
+|
+[
+a
+[
+Q
+D
+2
+1
+h
+-
+\
+a
+n
+J
+e
+F
+E
+<
+lV
+L
+"
+"
+2
+0B
+=
++
+2E
+k
+7T
+>
+7
+>
+BJ
+O
+)
+^
+e
+:
+jg
+4
+YZ
+(
+^
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+%
+T
+V
+\
+J
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+]
+-
+RfU
+#
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+i1
+%
+lH01
+K
+2F
+V
+E
+g
+s
+}
+f
+.
+M
++
+bF
+4Ws
+:
+d
+0
+2
+z
+x
+c
+f
+F
+p
+|
+w_
+#
+&
+x
+c
+f
+F
+(
+U
+x
+cd
+aa
+dd4
+/
+JL
+LN
+KMO
+K
+N
+-
+KJM
+/
+JMIM
+/
+JM5400
+-
+*
+I
+-
+L
+K
+-
+.
+002102
+g
+!
+C
+"
+_52
+Xe
+5
+e
+d
+e
+d
+1
+p0
+2
+1
+3
+2d3
+Z
+^
+Y
+j
+"
+s
+~
+AeQfzF
+F
+gzbNf
+B
+y
+&
+l
+{
+y
+/
+z
+#
+-
+N
+C
+Y
+~
+W
+.
+~
+]
+{
+n
+n
+_5
+H
+s2
+R
+x
+c
+d
+k
+_A
+?
+4
+M
+x
+c
+d
+bx
+z
+4p
+Jk
+v
+c
+j
+4
+d
+8
+/
+T
+>
+#
+T
+A
+A
+A
+*
+j
+K
+f
+;
+X
+"
+a
+{
+/
+_
+_
+1A1
diff --git a/testing/web-platform/tests/mathml/presentation-markup/radicals/root-parameters-2.html b/testing/web-platform/tests/mathml/presentation-markup/radicals/root-parameters-2.html
new file mode 100644
index 000000000000..165941561f5c
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/radicals/root-parameters-2.html
@@ -0,0 +1,675 @@
+<
+!
+DOCTYPE
+html
+>
+<
+html
+>
+<
+head
+>
+<
+meta
+charset
+=
+"
+utf
+-
+8
+"
+>
+<
+title
+>
+Radical
+parameters
+<
+/
+title
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+mathml
+-
+refresh
+.
+github
+.
+io
+/
+mathml
+-
+core
+/
+#
+radicals
+-
+msqrt
+-
+mroot
+"
+>
+<
+meta
+name
+=
+"
+assert
+"
+content
+=
+"
+Test
+edge
+kerning
+values
+for
+radicals
+.
+"
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharness
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharnessreport
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+mathml
+/
+support
+/
+feature
+-
+detection
+.
+js
+"
+>
+<
+/
+script
+>
+<
+style
+>
+font
+-
+face
+{
+font
+-
+family
+:
+radical
+-
+negativekernbeforedegree1000
+-
+rulethickness1000
+;
+src
+:
+url
+(
+"
+/
+fonts
+/
+math
+/
+radical
+-
+negativekernbeforedegree1000
+-
+rulethickness1000
+.
+woff
+"
+)
+;
+}
+font
+-
+face
+{
+font
+-
+family
+:
+radical
+-
+kernafterdegreeminus5000
+-
+rulethickness1000
+;
+src
+:
+url
+(
+"
+/
+fonts
+/
+math
+/
+radical
+-
+kernafterdegreeminus5000
+-
+rulethickness1000
+.
+woff
+"
+)
+;
+}
+math
+mspace
+{
+font
+-
+size
+:
+10px
+;
+}
+mspace
+{
+opacity
+:
+.
+5
+;
+}
+<
+/
+style
+>
+<
+script
+>
+var
+emToPx
+=
+10
+/
+1000
+;
+/
+/
+font
+-
+size
+:
+10px
+font
+.
+em
+=
+1000
+var
+epsilon
+=
+1
+;
+function
+getBox
+(
+aId
+)
+{
+return
+document
+.
+getElementById
+(
+aId
+)
+.
+getBoundingClientRect
+(
+)
+;
+}
+function
+runTests
+(
+)
+{
+test
+(
+function
+(
+)
+{
+assert_true
+(
+MathMLFeatureDetection
+.
+has_mspace
+(
+)
+)
+;
+assert_approx_equals
+(
+getBox
+(
+"
+index001
+"
+)
+.
+left
+-
+getBox
+(
+"
+mroot001
+"
+)
+.
+left
+0
+epsilon
+"
+should
+be
+clamped
+to
+0
+"
+)
+;
+}
+"
+RadicalKernBeforeDegree
+=
+-
+1em
+<
+0
+"
+)
+;
+test
+(
+function
+(
+)
+{
+assert_true
+(
+MathMLFeatureDetection
+.
+has_mspace
+(
+)
+)
+;
+var
+radicalSymbolWidth
+=
+1000
+*
+emToPx
+;
+var
+radicalLeft
+=
+getBox
+(
+"
+base002
+"
+)
+.
+left
+-
+radicalSymbolWidth
+;
+assert_approx_equals
+(
+getBox
+(
+"
+index002
+"
+)
+.
+right
+-
+radicalLeft
+30
+epsilon
+"
+should
+be
+clamped
+to
+3em
+"
+)
+;
+}
+"
+RadicalKernBeforeAfterDegree
+=
+-
+5em
+<
+-
+3em
+=
+-
+degree
+'
+s
+inline
+size
+"
+)
+;
+done
+(
+)
+;
+}
+setup
+(
+{
+explicit_done
+:
+true
+}
+)
+;
+window
+.
+addEventListener
+(
+"
+load
+"
+(
+)
+=
+>
+{
+document
+.
+fonts
+.
+ready
+.
+then
+(
+runTests
+)
+;
+}
+)
+;
+<
+/
+script
+>
+<
+/
+head
+>
+<
+body
+>
+<
+div
+id
+=
+"
+log
+"
+>
+<
+/
+div
+>
+<
+p
+>
+<
+math
+style
+=
+"
+font
+-
+family
+:
+radical
+-
+negativekernbeforedegree1000
+-
+rulethickness1000
+"
+>
+<
+mroot
+id
+=
+"
+mroot001
+"
+>
+<
+mspace
+id
+=
+"
+base001
+"
+height
+=
+"
+6em
+"
+width
+=
+"
+6em
+"
+style
+=
+"
+background
+:
+blue
+"
+/
+>
+<
+mspace
+id
+=
+"
+index001
+"
+height
+=
+"
+6em
+"
+width
+=
+"
+6em
+"
+style
+=
+"
+background
+:
+green
+"
+/
+>
+<
+/
+mroot
+>
+<
+/
+math
+>
+<
+/
+p
+>
+<
+hr
+/
+>
+<
+p
+>
+<
+math
+style
+=
+"
+font
+-
+family
+:
+radical
+-
+kernafterdegreeminus5000
+-
+rulethickness1000
+"
+>
+<
+mroot
+id
+=
+"
+mroot002
+"
+>
+<
+mspace
+id
+=
+"
+base002
+"
+height
+=
+"
+3em
+"
+width
+=
+"
+3em
+"
+style
+=
+"
+background
+:
+blue
+"
+/
+>
+<
+mspace
+id
+=
+"
+index002
+"
+height
+=
+"
+3em
+"
+width
+=
+"
+3em
+"
+style
+=
+"
+background
+:
+green
+"
+/
+>
+<
+/
+mroot
+>
+<
+/
+math
+>
+<
+/
+p
+>
+<
+/
+body
+>
+<
+/
+html
+>
diff --git a/testing/web-platform/tests/mathml/tools/radicals.py b/testing/web-platform/tests/mathml/tools/radicals.py
index 715f8700045a..f3667616f7d2 100644
--- a/testing/web-platform/tests/mathml/tools/radicals.py
+++ b/testing/web-platform/tests/mathml/tools/radicals.py
@@ -902,3 +902,112 @@
 (
 f
 )
+v1
+=
+1
+*
+mathfont
+.
+em
+v2
+=
+1
+*
+mathfont
+.
+em
+f
+=
+mathfont
+.
+create
+(
+"
+radical
+-
+negativekernbeforedegree
+%
+d
+-
+rulethickness
+%
+d
+"
+%
+(
+v1
+v2
+)
+"
+Copyright
+(
+c
+)
+2020
+Igalia
+S
+.
+L
+.
+"
+)
+createStretchyRadical
+(
+f
+)
+f
+.
+math
+.
+RadicalDegreeBottomRaisePercent
+=
+0
+f
+.
+math
+.
+RadicalDisplayStyleVerticalGap
+=
+0
+f
+.
+math
+.
+RadicalExtraAscender
+=
+0
+f
+.
+math
+.
+RadicalKernAfterDegree
+=
+0
+f
+.
+math
+.
+RadicalKernBeforeDegree
+=
+-
+v1
+f
+.
+math
+.
+RadicalRuleThickness
+=
+v2
+f
+.
+math
+.
+RadicalVerticalGap
+=
+0
+mathfont
+.
+save
+(
+f
+)