diff --git a/components/style/properties/longhand/position.mako.rs b/components/style/properties/longhand/position.mako.rs
index 263e45579f33..590b7cb8980a 100644
--- a/components/style/properties/longhand/position.mako.rs
+++ b/components/style/properties/longhand/position.mako.rs
@@ -158,6 +158,7 @@ ${helpers.predefined_type("flex-basis",
                               "computed::LengthOrPercentageOrAuto::Auto",
                               "parse_non_negative",
                               spec=spec % size,
+                              allow_quirks=not logical,
                               animation_value_type="ComputedValue", logical = logical)}
     % if product == "gecko":
         % for min_max in ["min", "max"]:
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index 6a66e658aef0..2581db7290db 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -1360,7 +1360,16 @@ impl LengthOrPercentageOrAuto {
     /// Parse a non-negative length, percentage, or auto.
     #[inline]
     pub fn parse_non_negative(context: &ParserContext, input: &mut Parser) -> Result<LengthOrPercentageOrAuto, ()> {
-        Self::parse_internal(context, input, AllowedLengthType::NonNegative, AllowQuirks::No)
+        Self::parse_non_negative_quirky(context, input, AllowQuirks::No)
+    }
+
+    /// Parse a non-negative length, percentage, or auto.
+    #[inline]
+    pub fn parse_non_negative_quirky(context: &ParserContext,
+                                     input: &mut Parser,
+                                     allow_quirks: AllowQuirks)
+                                     -> Result<Self, ()> {
+        Self::parse_internal(context, input, AllowedLengthType::NonNegative, allow_quirks)
     }
 
     /// Returns the `auto` value.
diff --git a/tests/wpt/metadata/quirks-mode/unitless-length.html.ini b/tests/wpt/metadata/quirks-mode/unitless-length.html.ini
index 95010cb9d615..385892d38e5e 100644
--- a/tests/wpt/metadata/quirks-mode/unitless-length.html.ini
+++ b/tests/wpt/metadata/quirks-mode/unitless-length.html.ini
@@ -12,9 +12,6 @@
     expected:
       if os == "mac": FAIL
 
-  [height: 1 (quirks)]
-    expected: FAIL
-
   [letter-spacing: 1 (quirks)]
     expected: FAIL
 
@@ -75,9 +72,6 @@
   [vertical-align: 1 (quirks)]
     expected: FAIL
 
-  [width: 1 (quirks)]
-    expected: FAIL
-
   [word-spacing: 1 (quirks)]
     expected: FAIL
 
@@ -93,9 +87,6 @@
     expected:
       if os == "mac": FAIL
 
-  [height: +1 (quirks)]
-    expected: FAIL
-
   [letter-spacing: +1 (quirks)]
     expected: FAIL
 
@@ -156,9 +147,6 @@
   [vertical-align: +1 (quirks)]
     expected: FAIL
 
-  [width: +1 (quirks)]
-    expected: FAIL
-
   [word-spacing: +1 (quirks)]
     expected: FAIL
 
@@ -225,9 +213,6 @@
     expected:
       if os == "mac": FAIL
 
-  [height: 1.5 (quirks)]
-    expected: FAIL
-
   [letter-spacing: 1.5 (quirks)]
     expected: FAIL
 
@@ -288,9 +273,6 @@
   [vertical-align: 1.5 (quirks)]
     expected: FAIL
 
-  [width: 1.5 (quirks)]
-    expected: FAIL
-
   [word-spacing: 1.5 (quirks)]
     expected: FAIL
 
@@ -306,9 +288,6 @@
     expected:
       if os == "mac": FAIL
 
-  [height: +1.5 (quirks)]
-    expected: FAIL
-
   [letter-spacing: +1.5 (quirks)]
     expected: FAIL
 
@@ -369,9 +348,6 @@
   [vertical-align: +1.5 (quirks)]
     expected: FAIL
 
-  [width: +1.5 (quirks)]
-    expected: FAIL
-
   [word-spacing: +1.5 (quirks)]
     expected: FAIL