diff --git a/components/layout/multicol.rs b/components/layout/multicol.rs
index 22f8e3e24ab..3659d50e219 100644
--- a/components/layout/multicol.rs
+++ b/components/layout/multicol.rs
@@ -106,9 +106,8 @@ impl Flow for MulticolFlow {
         {
             let column_style = self.block_flow.fragment.style.get_column();
 
-            // FIXME(#20498): This should support percentages too.
             let column_gap = match column_style.column_gap {
-                Either::First(len) => len.into(),
+                Either::First(len) => len.0.to_pixel_length(content_inline_size).into(),
                 Either::Second(_normal) => self.block_flow.fragment.style.get_font().font_size.size(),
             };
 
diff --git a/components/style/properties/longhand/column.mako.rs b/components/style/properties/longhand/column.mako.rs
index 9113479218b..5ed8164e7eb 100644
--- a/components/style/properties/longhand/column.mako.rs
+++ b/components/style/properties/longhand/column.mako.rs
@@ -30,17 +30,14 @@ ${helpers.predefined_type(
 )}
 
 
-<%
-# FIXME(#20498): Servo should support percentages in column-gap.
-col_gap_type = "NonNegativeLengthOrPercentageOrNormal" if product == "gecko" else "NonNegativeLengthOrNormal"
-%>
+
 ${helpers.predefined_type(
     "column-gap",
-    "length::%s" % col_gap_type,
+    "length::NonNegativeLengthOrPercentageOrNormal",
     "Either::Second(Normal)",
     extra_prefixes="moz",
     servo_pref="layout.columns.enabled",
-    animation_value_type=col_gap_type,
+    animation_value_type="NonNegativeLengthOrPercentageOrNormal",
     spec="https://drafts.csswg.org/css-multicol/#propdef-column-gap",
     servo_restyle_damage = "reflow",
 )}