diff --git a/src/main/java/io/vertx/core/http/impl/HttpUtils.java b/src/main/java/io/vertx/core/http/impl/HttpUtils.java
index de10da83aec..608f36ba47d 100644
--- a/src/main/java/io/vertx/core/http/impl/HttpUtils.java
+++ b/src/main/java/io/vertx/core/http/impl/HttpUtils.java
@@ -19,6 +19,7 @@
 import io.netty.handler.codec.http2.Http2Settings;
 import io.netty.util.AsciiString;
 import io.netty.util.CharsetUtil;
+import io.netty.util.internal.PlatformDependent;
 import io.vertx.core.AsyncResult;
 import io.vertx.core.Future;
 import io.vertx.core.Handler;
@@ -882,7 +883,9 @@ private static void validateAsciiHeaderValue(AsciiString value) {
     int off = value.arrayOffset();
     int end = off + length;
 
-    for (int index = off; index < end; index++) {
+    // DON'T REMOVE 'off == 0? 0 : off' as it's a micro-optimization to reduce the range checks
+    // since AsciiString(s) often (if not always) have offset == 0
+    for (int index = off == 0? 0 : off; index < end; index++) {
       int latinChar = asciiChars[index] & 0xFF;
       if (latinChar == 0x7F) {
         throw new IllegalArgumentException("a header value contains a prohibited character '127': " + value);