diff --git a/tools/perf/util/perf_regs.h b/tools/perf/util/perf_regs.h
index c9319f8d17a6..f732e3af2bd4 100644
--- a/tools/perf/util/perf_regs.h
+++ b/tools/perf/util/perf_regs.h
@@ -34,7 +34,7 @@ int perf_reg_value(u64 *valp, struct regs_dump *regs, int id);
 
 static inline const char *perf_reg_name(int id __maybe_unused)
 {
-	return NULL;
+	return "unknown";
 }
 
 static inline int perf_reg_value(u64 *valp __maybe_unused,