diff --git a/mod.js b/mod.js
index be6b3825..0f73496d 100644
--- a/mod.js
+++ b/mod.js
@@ -1151,6 +1151,9 @@ var matchers = (function () {
     ")[,|\\s]+(" +
     CSS_UNIT +
     ")\\s*\\)?";
+  // Fourth value (alpha) is optional so rgba()/hsla()/hsva() match CSS
+  // Color 4, where rgb/rgba and hsl/hsla are aliases. Slash is allowed as
+  // the separator before alpha (`rgba(255 0 0 / 0.5)`).
   var PERMISSIVE_MATCH4 =
     "[\\s|\\(]+(" +
     CSS_UNIT +
@@ -1158,9 +1161,9 @@ var matchers = (function () {
     CSS_UNIT +
     ")[,|\\s]+(" +
     CSS_UNIT +
-    ")[,|\\s]+(" +
+    ")(?:[,|\\s/]+(" +
     CSS_UNIT +
-    ")\\s*\\)?";
+    "))?\\s*\\)?";
 
   return {
     CSS_UNIT: new RegExp(CSS_UNIT),
diff --git a/test.js b/test.js
index d6003428..aef121cd 100644
--- a/test.js
+++ b/test.js
@@ -352,6 +352,19 @@ Deno.test("RGB Text Parsing", function () {
     tinycolor.equals({ r: 200, g: 100, b: 0, a: 0.4 }, "rgba 200 100 0 .4")
   );
   assert(!tinycolor.equals({ r: 199, g: 100, b: 0 }, "rgba 200 100 0 1"));
+  assert(
+    tinycolor.equals({ r: 200, g: 100, b: 0 }, "rgba(200, 100, 0)"),
+    "rgba without alpha"
+  );
+  assert(tinycolor.equals({ r: 200, g: 100, b: 0 }, "rgba 200 100 0"));
+  assert(
+    tinycolor("rgba(255, 0, 0)").isValid(),
+    "rgba without alpha is valid"
+  );
+  assert(
+    tinycolor.equals({ r: 255, g: 0, b: 0, a: 0.5 }, "rgba(255 0 0 / 0.5)"),
+    "rgba with slash-separated alpha"
+  );
 
   assert(!tinycolor.equals({ r: 199, g: 100, b: 0 }, "rgb(200, 100, 0)"));
   assert(!tinycolor.equals({ r: 199, g: 100, b: 0 }, "rgb 200 100 0"));
@@ -411,6 +424,13 @@ Deno.test("Percentage RGB Text Parsing", function () {
       "rgba 90% 45% 0% .4"
     )
   );
+  assert(
+    tinycolor.equals(
+      { r: "90%", g: "45%", b: "0%" },
+      "rgba(90%, 45%, 0%)"
+    ),
+    "percentage rgba without alpha"
+  );
   assert(
     !tinycolor.equals({ r: "89%", g: "45%", b: "0%" }, "rgba 90% 45% 0% 1")
   );
@@ -482,6 +502,11 @@ Deno.test("HSL parsing", function () {
     "hsl(100, 20%, 10%)",
     "problematic hsl"
   );
+  assertEquals(
+    tinycolor("hsla(251, 100%, 38%)").toHslString(),
+    "hsl(251, 100%, 38%)",
+    "hsla without alpha"
+  );
 });
 
 Deno.test("Hex Parsing", function () {
@@ -511,6 +536,11 @@ Deno.test("HSV Parsing", function () {
     tinycolor("hsva 251.1 0.887 0.918 0.5").toHsvString(),
     "hsva(251, 89%, 92%, 0.5)"
   );
+  assertEquals(
+    tinycolor("hsva 251.1 0.887 0.918").toHsvString(),
+    "hsv(251, 89%, 92%)",
+    "hsva without alpha"
+  );
 });
 
 Deno.test("Invalid Parsing", function () {