diff --git a/Common/s2j/s2jdef.h b/Common/s2j/s2jdef.h
index 7e15737e7..9002b088e 100644
--- a/Common/s2j/s2jdef.h
+++ b/Common/s2j/s2jdef.h
@@ -52,7 +52,8 @@ typedef struct {
     
 #define S2J_STRUCT_GET_STRING_ELEMENT_N(to_struct, from_json, _element, n) \
         json_temp = cJSON_GetObjectItem(from_json, #_element); \
-        if (json_temp && n > 1) strncpy((to_struct)->_element, json_temp->valuestring, n-1);
+        if (json_temp && json_temp->valuestring && n > 1)\
+            strncpy((to_struct)->_element, json_temp->valuestring, n-1);
 
 #define S2J_STRUCT_GET_double_ELEMENT(to_struct, from_json, _element) \
     json_temp = cJSON_GetObjectItem(from_json, #_element); \