diff --git a/oniggnu.h b/oniggnu.h
index e63374efc0..0882577760 100644
--- a/oniggnu.h
+++ b/oniggnu.h
@@ -31,6 +31,10 @@
 
 #include "oniguruma.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #define MBCTYPE_ASCII         0
 #define MBCTYPE_EUC           1
 #define MBCTYPE_SJIS          2
@@ -107,4 +111,8 @@ void re_free_registers P_((struct re_registers*));
 ONIG_EXTERN
 int re_alloc_pattern P_((struct re_pattern_buffer**));  /* added */
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* ONIGGNU_H */