diff --git a/include/ply.h b/include/ply.h
index 9ea9d29..4671a85 100644
--- a/include/ply.h
+++ b/include/ply.h
@@ -49,20 +49,20 @@ typedef struct PlyElementStruct {
 } PlyElement;
 
 
-char* ply_formats[] = {
+const char* const ply_formats[] = {
   "ascii",
   "binary_little_endian",
   "binary_big_endian"
 };
 
-char* ply_header_items[] = {
+const char* const ply_header_items[] = {
   "comment",
   "end_header",
   "element",
   "property",
 };
 
-char* ply_type_strings[] = {
+const char* const ply_type_strings[] = {
   "char",
   "uchar",
   "short",