diff --git a/src/backend/libpq/pqformat.c b/src/backend/libpq/pqformat.c
index a6f990c..03b7404 100644
--- a/src/backend/libpq/pqformat.c
+++ b/src/backend/libpq/pqformat.c
@@ -328,11 +328,16 @@ void
 pq_begintypsend(StringInfo buf)
 {
 	initStringInfo(buf);
-	/* Reserve four bytes for the bytea length word */
-	appendStringInfoCharMacro(buf, '\0');
-	appendStringInfoCharMacro(buf, '\0');
-	appendStringInfoCharMacro(buf, '\0');
-	appendStringInfoCharMacro(buf, '\0');
+
+	/*
+	 * Reserve four bytes for the bytea length word.  We don't need to fill
+	 * them with anything (pq_endtypsend will do that), and this function is
+	 * enough of a hot spot that it's worth cheating to save some cycles. Note
+	 * in particular that we don't bother to guarantee that the buffer is
+	 * null-terminated.
+	 */
+	Assert(buf->maxlen > 4);
+	buf->len = 4;
 }
 
 /* --------------------------------