diff --git a/protobuf.c b/protobuf.c
index d6f70b1..c73c697 100644
--- a/protobuf.c
+++ b/protobuf.c
@@ -86,7 +86,7 @@ SIMPLE_PB* read_pb_into(FILE* fp, SIMPLE_PB* spb) {
     return spb;
 }
 
-int set_pb(FILE* fp, uint32_t* items_len, uint32_t struct_len, void* target) {
+int set_pb(FILE* fp, const uint32_t* items_len, uint32_t struct_len, const void* target) {
     uint32_t offset = 0;
     uint32_t i = 0;
     char* p = (char*)target;
diff --git a/simple_protobuf.h b/simple_protobuf.h
index 8fa23c7..de3bb02 100644
--- a/simple_protobuf.h
+++ b/simple_protobuf.h
@@ -16,7 +16,7 @@ uint32_t get_pb_len(FILE* fp);
 
 SIMPLE_PB* read_pb_into(FILE* fp, SIMPLE_PB* spb);
 
-int set_pb(FILE* fp, uint32_t* items_len, uint32_t struct_len, void* target);
+int set_pb(FILE* fp, const uint32_t* items_len, uint32_t struct_len, const void* target);
 
 // items_len = align_struct(uint32_t struct_size, uint32_t items_cnt, void* item_addr1, void* item_addr2...)
 uint32_t* align_struct(uint32_t struct_size, uint32_t items_cnt, ...);