diff --git a/css-values-3/Overview.bs b/css-values-3/Overview.bs
index 203d1beb720c..5a2a44dafd9f 100644
--- a/css-values-3/Overview.bs
+++ b/css-values-3/Overview.bs
@@ -1131,6 +1131,8 @@ Absolute lengths: the ''cm'', ''mm'', ''Q'', ''in'', ''pt'', ''pc'', ''px'' unit
 	(This change was made because too much existing content relies on the assumption of 96dpi,
 	and breaking that assumption broke the content.)
 
+	Note: Values are case-insensitive and serialize as lower case, for example 1Q serializes as 1q.
+
 	The <dfn export>reference pixel</dfn> is the visual angle of one pixel on a device with a pixel density of 96dpi
 	and a distance from the reader of an arm's length.
 	For a nominal arm's length of 28 inches,
@@ -1301,6 +1303,8 @@ Frequency Units: the <<frequency>> type and ''Hz'', ''kHz'' units</h3>
 	All <<frequency>> units are <a>compatible</a>,
 	and ''hz'' is their <a>canonical unit</a>.
 
+	Note: Values are case-insensitive and serialize as lower case, for example 1Hz serializes as 1hz.
+
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diff --git a/css-values-4/Overview.bs b/css-values-4/Overview.bs
index 55f34c923b35..62c2bf243881 100644
--- a/css-values-4/Overview.bs
+++ b/css-values-4/Overview.bs
@@ -1228,6 +1228,8 @@ Absolute lengths: the ''cm'', ''mm'', ''Q'', ''in'', ''pt'', ''pc'', ''px'' unit
 	(This change was made because too much existing content relies on the assumption of 96dpi,
 	and breaking that assumption broke the content.)
 
+	Note: Values are case-insensitive and serialize as lower case, for example 1Q serializes as 1q.
+
 	The <dfn export>reference pixel</dfn> is the visual angle of one pixel on a device with a pixel density of 96dpi
 	and a distance from the reader of an arm's length.
 	For a nominal arm's length of 28 inches,
@@ -1398,6 +1400,8 @@ Frequency Units: the <<frequency>> type and ''Hz'', ''kHz'' units</h3>
 	All <<frequency>> units are <a>compatible</a>,
 	and ''hz'' is their <a>canonical unit</a>.
 
+	Note: Values are case-insensitive and serialize as lower case, for example 1Hz serializes as 1hz.
+
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