diff --git a/alts/src/main/java/io/grpc/alts/internal/AltsTsiFrameProtector.java b/alts/src/main/java/io/grpc/alts/internal/AltsTsiFrameProtector.java
index 67d6637a1303..42342e30a972 100644
--- a/alts/src/main/java/io/grpc/alts/internal/AltsTsiFrameProtector.java
+++ b/alts/src/main/java/io/grpc/alts/internal/AltsTsiFrameProtector.java
@@ -206,7 +206,7 @@ static final class Unprotector {
       this.crypter = crypter;
       this.suffixBytes = crypter.getSuffixLength();
       this.header = alloc.directBuffer(HEADER_BYTES);
-      this.firstFrameTag = alloc.directBuffer(suffixBytes);
+      this.firstFrameTag = alloc.compositeDirectBuffer(suffixBytes);
     }
 
     private void addUnhandled(ByteBuf in) {