diff --git a/components/style/properties/longhand/inherited_table.mako.rs b/components/style/properties/longhand/inherited_table.mako.rs
index 3069482976ed..e464d9433f61 100644
--- a/components/style/properties/longhand/inherited_table.mako.rs
+++ b/components/style/properties/longhand/inherited_table.mako.rs
@@ -26,6 +26,7 @@ ${helpers.single_keyword("caption-side", "top bottom",
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
+    use values::specified::{AllowQuirks, Length};
 
     pub mod computed_value {
         use app_units::Au;
@@ -60,8 +61,8 @@ ${helpers.single_keyword("caption-side", "top bottom",
     #[derive(Clone, Debug, PartialEq)]
     #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
     pub struct SpecifiedValue {
-        pub horizontal: specified::Length,
-        pub vertical: Option<specified::Length>,
+        pub horizontal: Length,
+        pub vertical: Option<Length>,
     }
 
     #[inline]
@@ -117,11 +118,11 @@ ${helpers.single_keyword("caption-side", "top bottom",
     pub fn parse(context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue,()> {
         let mut first = None;
         let mut second = None;
-        match specified::Length::parse_non_negative(context, input) {
+        match Length::parse_non_negative_quirky(context, input, AllowQuirks::Yes) {
             Err(()) => (),
             Ok(length) => {
                 first = Some(length);
-                if let Ok(len) = input.try(|input| specified::Length::parse_non_negative(context, input)) {
+                if let Ok(len) = input.try(|i| Length::parse_non_negative_quirky(context, i, AllowQuirks::Yes)) {
                     second = Some(len);
                 }
             }
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index e161b5fc5891..424e65532798 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -563,13 +563,17 @@ impl Length {
     }
 
     #[inline]
-    fn parse_internal(context: &ParserContext, input: &mut Parser, num_context: AllowedLengthType)
+    fn parse_internal(context: &ParserContext,
+                      input: &mut Parser,
+                      num_context: AllowedLengthType,
+                      allow_quirks: AllowQuirks)
                       -> Result<Length, ()> {
         match try!(input.next()) {
             Token::Dimension(ref value, ref unit) if num_context.is_ok(value.value) =>
                 Length::parse_dimension(context, value.value, unit),
-            Token::Number(ref value) => {
-                if value.value != 0. && !context.length_parsing_mode.allows_unitless_lengths() {
+            Token::Number(ref value) if num_context.is_ok(value.value) => {
+                if value.value != 0. && !context.length_parsing_mode.allows_unitless_lengths() &&
+                   !allow_quirks.allowed(context.quirks_mode) {
                     return Err(())
                 }
                 Ok(Length::NoCalc(NoCalcLength::Absolute(AbsoluteLength::Px(value.value))))
@@ -585,7 +589,16 @@ impl Length {
     /// Parse a non-negative length
     #[inline]
     pub fn parse_non_negative(context: &ParserContext, input: &mut Parser) -> Result<Length, ()> {
-        Self::parse_internal(context, input, AllowedLengthType::NonNegative)
+        Self::parse_non_negative_quirky(context, input, AllowQuirks::No)
+    }
+
+    /// Parse a non-negative length, allowing quirks.
+    #[inline]
+    pub fn parse_non_negative_quirky(context: &ParserContext,
+                                     input: &mut Parser,
+                                     allow_quirks: AllowQuirks)
+                                     -> Result<Length, ()> {
+        Self::parse_internal(context, input, AllowedLengthType::NonNegative, allow_quirks)
     }
 
     /// Get an absolute length from a px value.
@@ -605,7 +618,7 @@ impl Length {
 
 impl Parse for Length {
     fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
-        Self::parse_internal(context, input, AllowedLengthType::All)
+        Self::parse_internal(context, input, AllowedLengthType::All, AllowQuirks::No)
     }
 }
 
@@ -616,7 +629,7 @@ impl<T: Parse> Either<Length, T> {
         if let Ok(v) = input.try(|input| T::parse(context, input)) {
             return Ok(Either::Second(v));
         }
-        Length::parse_internal(context, input, AllowedLengthType::NonNegative).map(Either::First)
+        Length::parse_internal(context, input, AllowedLengthType::NonNegative, AllowQuirks::No).map(Either::First)
     }
 }
 
diff --git a/tests/wpt/metadata/quirks-mode/unitless-length.html.ini b/tests/wpt/metadata/quirks-mode/unitless-length.html.ini
index 9b8f785c3ce8..2be0a018e450 100644
--- a/tests/wpt/metadata/quirks-mode/unitless-length.html.ini
+++ b/tests/wpt/metadata/quirks-mode/unitless-length.html.ini
@@ -1,8 +1,5 @@
 [unitless-length.html]
   type: testharness
-  [border-spacing: 1 (quirks)]
-    expected: FAIL
-
   [border-top-width: 1 (quirks)]
     expected: FAIL
 
@@ -102,9 +99,6 @@
   [word-spacing: 1 (quirks)]
     expected: FAIL
 
-  [border-spacing: +1 (quirks)]
-    expected: FAIL
-
   [border-top-width: +1 (quirks)]
     expected: FAIL
 
@@ -255,9 +249,6 @@
   [word-spacing: -1 (quirks)]
     expected: FAIL
 
-  [border-spacing: 1.5 (quirks)]
-    expected: FAIL
-
   [border-top-width: 1.5 (quirks)]
     expected: FAIL
 
@@ -357,9 +348,6 @@
   [word-spacing: 1.5 (quirks)]
     expected: FAIL
 
-  [border-spacing: +1.5 (quirks)]
-    expected: FAIL
-
   [border-top-width: +1.5 (quirks)]
     expected: FAIL
 
@@ -1248,9 +1236,6 @@
   [top: calc(2 * 2px) (standards)]
     expected: FAIL
 
-  [border-spacing: 1px 2 (quirks)]
-    expected: FAIL
-
   [border-width: 1px 2 (quirks)]
     expected: FAIL
 
@@ -1260,9 +1245,6 @@
   [padding: 1px 2 (quirks)]
     expected: FAIL
 
-  [border-spacing: 1 2px (quirks)]
-    expected: FAIL
-
   [border-width: 1 2px (quirks)]
     expected: FAIL
 
@@ -1272,9 +1254,6 @@
   [padding: 1 2px (quirks)]
     expected: FAIL
 
-  [border-spacing: 1 +2 (quirks)]
-    expected: FAIL
-
   [border-width: 1 +2 (quirks)]
     expected: FAIL