diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 63b6f8c8edf28715d0d2e74cddd284e0d4d093a0..df99ebe852ae1b54e69db2875b188870eaf13e86 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -124,7 +124,7 @@ struct event_format *event_format__new(const char *sys, const char *name)
 			bf = nbf;
 		}
 
-		n = read(fd, bf + size, BUFSIZ);
+		n = read(fd, bf + size, alloc_size - size);
 		if (n < 0)
 			goto out_free_bf;
 		size += n;