diff --git a/adb/adb_io.cpp b/adb/adb_io.cpp
index 6cc274b..e6fefda 100644
--- a/adb/adb_io.cpp
+++ b/adb/adb_io.cpp
@@ -38,7 +38,8 @@
 
     // The cost of sending two strings outweighs the cost of formatting.
     // "adb sync" performance is affected by this.
-    return WriteFdFmt(fd, "%04x%.*s", length, length, s.c_str());
+    auto str = android::base::StringPrintf("%04x", length).append(s);
+    return WriteFdExactly(fd, str);
 }
 
 bool ReadProtocolString(int fd, std::string* s, std::string* error) {