diff --git a/.changeset/curly-jars-punch.md b/.changeset/curly-jars-punch.md
new file mode 100644
index 000000000..b6278b9f3
--- /dev/null
+++ b/.changeset/curly-jars-punch.md
@@ -0,0 +1,6 @@
+---
+'@emotion/serialize': patch
+'@emotion/utils': patch
+---
+
+Minor performance improvement
diff --git a/packages/serialize/src/index.ts b/packages/serialize/src/index.ts
index 8e69a588b..dcae2895d 100644
--- a/packages/serialize/src/index.ts
+++ b/packages/serialize/src/index.ts
@@ -365,7 +365,7 @@ function createStringFromObject(
   return string
 }
 
-let labelPattern = /label:\s*([^\s;\n{]+)\s*(;|$)/g
+let labelPattern = /label:\s*([^\s;{]+)\s*(;|$)/g
 
 let sourceMapPattern: RegExp | undefined
 if (isDevelopment) {
diff --git a/packages/utils/src/index.ts b/packages/utils/src/index.ts
index 88dc29da9..b80551376 100644
--- a/packages/utils/src/index.ts
+++ b/packages/utils/src/index.ts
@@ -11,7 +11,7 @@ export function getRegisteredStyles(
   classNames.split(' ').forEach(className => {
     if (registered[className] !== undefined) {
       registeredStyles.push(`${registered[className]};`)
-    } else {
+    } else if (className) {
       rawClassName += `${className} `
     }
   })