diff --git a/core/opentype-parser.lua b/core/opentype-parser.lua
index b6362fa0c..a16f2f02a 100644
--- a/core/opentype-parser.lua
+++ b/core/opentype-parser.lua
@@ -433,6 +433,18 @@ local function parseMath(s)
   }
 end
 
+local function parsePost(s)
+  if s:len() <= 0 then return end
+  local fd = vstruct.cursor(s)
+  local header = vstruct.read(">majorVersion:u2 minorVersion:u2 italicAngle:i4 underlinePosition:i2 underlineThickness:i2 isFixedPitch:u4", fd)
+  local italicAngle = header.italicAngle / 65536 -- 1 << 16
+  return {
+    italicAngle = italicAngle,
+    underlinePosition = header.underlinePosition,
+    underlineThickness = header.underlineThickness
+  }
+end
+
 local parseFont = function(face)
   if not face.font then
     local font = {}
@@ -443,6 +455,7 @@ local parseFont = function(face)
     font.cpal = parseCpal(hb.get_table(face.data, face.index, "CPAL"))
     font.svg  = parseSvg(hb.get_table(face.data, face.index, "SVG"))
     font.math = parseMath(hb.get_table(face.data, face.index, "MATH"))
+    font.post = parsePost(hb.get_table(face.data, face.index, "post"))
     face.font = font
   end
   return face.font
diff --git a/packages/rules.lua b/packages/rules.lua
index 65f7c4b48..db6dfad18 100644
--- a/packages/rules.lua
+++ b/packages/rules.lua
@@ -34,13 +34,21 @@ SILE.registerCommand("fullrule", function (options, _)
 end, "Draw a full width hrule centered on the current line")
 
 SILE.registerCommand("underline", function (_, content)
+  local ot = SILE.require("core/opentype-parser")
+  local fontoptions = SILE.font.loadDefaults({})
+  local face = SILE.font.cache(fontoptions, SILE.shaper.getFace)
+  local font = ot.parseFont(face)
+  local upem = font.head.unitsPerEm
+  local underlinePosition = -font.post.underlinePosition / upem * fontoptions.size
+  local underlineThickness = font.post.underlineThickness / upem * fontoptions.size
+
   local hbox = SILE.call("hbox", {}, content)
   local gl = SILE.length() - hbox.width
-  SILE.call("lower", {height = "0.5pt"}, function()
-    SILE.call("hrule", {width = gl.length, height = "0.5pt"})
+  SILE.call("lower", {height = SU.cast("measurement", underlinePosition)}, function()
+    SILE.call("hrule", {width = gl.length, height = underlineThickness})
   end)
   SILE.typesetter:pushGlue({width = hbox.width})
-end, "Underlines some content (badly)")
+end, "Underlines some content")
 
 SILE.registerCommand("boxaround", function (_, content)
   local hbox = SILE.call("hbox", {}, content)
diff --git a/tests/bug-1259.expected b/tests/bug-1259.expected
new file mode 100644
index 000000000..b3417022e
--- /dev/null
+++ b/tests/bug-1259.expected
@@ -0,0 +1,36 @@
+Set paper size 	419.5275636	595.275597
+Begin page
+Mx 	20.9764
+My 	37.3321
+Set font 	Gentium Plus;10;400;;normal;;LTR
+T	43 68 89 72 w=20.6787	(Have)
+Mx 	44.3212
+T	86 82 80 72 w=21.5430	(some)
+Mx 	68.5303
+T	88 81 71 72 85 79 76 81 76 81 74 w=48.6377	(underlining)
+Draw line	117.1680	38.0646	-48.6377	0.4883
+Mx 	119.8342
+T	85 72 79 68 87 76 89 72 w=31.5820	(relative)
+Mx 	154.0823
+T	87 82 w=8.4717	(to)
+Mx 	165.2201
+T	73 82 81 87 w=17.0996	(font)
+Mx 	182.3197
+T	17 w=2.2900	(.)
+Mx 	20.9764
+My 	73.3321
+Set font 	Libertinus Serif;30;400;;normal;;LTR
+T	54 84 70 w=44.9400	(Use)
+Mx 	72.4164
+T	86 79 69 70 83 77 74 79 74 79 72 w=143.6400	(underlining)
+Draw line	216.0564	74.4721	-143.6400	1.2000
+Mx 	222.5564
+T	74 79 w=24.3900	(in)
+Mx 	253.4464
+T	66 79 80 85 73 70 83 w=95.2800	(another)
+Mx 	355.2264
+T	71 80 79 85 w=50.1600	(font)
+Mx 	405.3864
+T	15 w=6.6000	(.)
+End page
+Finish
diff --git a/tests/bug-1259.sil b/tests/bug-1259.sil
new file mode 100644
index 000000000..dcc6150e8
--- /dev/null
+++ b/tests/bug-1259.sil
@@ -0,0 +1,11 @@
+\begin[papersize=a5]{document}
+\neverindent
+\nofolios
+\script[src=packages/rules]
+
+Have some \underline{underlining} relative to font.
+
+\font[size=30pt,family=Libertinus Serif]
+
+Use \underline{underlining} in another font.
+\end{document}