diff --git a/core/modules/filters/colour-ops.js b/core/modules/filters/colour-ops.js
index f03841a0f4..9a38ee36de 100644
--- a/core/modules/filters/colour-ops.js
+++ b/core/modules/filters/colour-ops.js
@@ -25,6 +25,10 @@ exports["colour-get-oklch"] = makeSerialColourOperator(function (colour, operato
 	var prop = ((operator.suffixes || [])[0] || ["l"])[0];
 	if(["l","c","h"].indexOf(prop) !== -1) {
 		colour = colour.oklch[prop];
+		// Hue is null for achromatic colours
+		if(colour === null || colour === undefined || Number.isNaN(colour)) {
+			return "";
+		}
 	}
 	return colour.toString();
 });
@@ -63,6 +67,9 @@ exports["colour-best-contrast"] = makeParallelColourOperator(function (colours,
 		return [];
 	}
 	var targetColour = colours[colours.length - 1];
+	if(!targetColour) {
+		return [];
+	}
 	for(var t=0; t<colours.length; t++) {
 		var colour = colours[t];
 		if(colour) {
diff --git a/editions/test/tiddlers/tests/data/operators/colour/ColourBestContrastInvalidTarget.tid b/editions/test/tiddlers/tests/data/operators/colour/ColourBestContrastInvalidTarget.tid
new file mode 100644
index 0000000000..747c238db2
--- /dev/null
+++ b/editions/test/tiddlers/tests/data/operators/colour/ColourBestContrastInvalidTarget.tid
@@ -0,0 +1,17 @@
+title: Operators/Colour/ColourBestContrastInvalidTarget
+description: colour-best-contrast with an unparseable target colour returns nothing instead of crashing
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\parsermode inline
+<$text text={{{ [subfilter{Filter}] +[count[]] }}}/>
++
+title: Filter
+
+[[red]] [[blue]] [[notacolour]] +[colour-best-contrast[]]
++
+title: ExpectedResult
+
+0
\ No newline at end of file
diff --git a/editions/test/tiddlers/tests/data/operators/colour/ColourGetOklchAchromatic.tid b/editions/test/tiddlers/tests/data/operators/colour/ColourGetOklchAchromatic.tid
new file mode 100644
index 0000000000..e08f674f6d
--- /dev/null
+++ b/editions/test/tiddlers/tests/data/operators/colour/ColourGetOklchAchromatic.tid
@@ -0,0 +1,20 @@
+title: Operators/Colour/ColourGetOklchAchromatic
+description: colour-get-oklch hue of achromatic colours returns empty instead of crashing
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\parsermode inline
+<$text text={{{ [subfilter{Filter}] }}}/>
++
+title: Filter
+
+=[[white]colour-get-oklch:h[]]
+=[[#808080]colour-get-oklch:h[]]
+=[[red]colour-get-oklch:h[]fixed[3]]
++[join[,]]
++
+title: ExpectedResult
+
+,,29.234
\ No newline at end of file