diff --git a/okhttp/src/main/java/io/grpc/okhttp/OkHttpServerTransport.java b/okhttp/src/main/java/io/grpc/okhttp/OkHttpServerTransport.java
index 5ec393e1073..f908e6a231a 100644
--- a/okhttp/src/main/java/io/grpc/okhttp/OkHttpServerTransport.java
+++ b/okhttp/src/main/java/io/grpc/okhttp/OkHttpServerTransport.java
@@ -458,7 +458,7 @@ private static String asciiString(ByteString value) {
     // utf8() string is cached in ByteString, so we prefer it when the contents are ASCII. This
     // provides benefit if the header was reused via HPACK.
     for (int i = 0; i < value.size(); i++) {
-      if (value.getByte(i) >= 0x80) {
+      if (value.getByte(i) < 0) {
         return value.string(GrpcUtil.US_ASCII);
       }
     }