diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 819979b1..086f7b6e 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -2069,7 +2069,7 @@ check_ca_required(const struct options *options)
         return;
     }
 
-    const char* str = "You must define CA file (--ca)"
+    const char* const str = "You must define CA file (--ca)"
 #ifndef ENABLE_CRYPTO_MBEDTLS
         " or CA path (--capath)"
 #endif