diff --git a/node.c b/node.c
index 79ef00f1b7..9844401331 100644
--- a/node.c
+++ b/node.c
@@ -53,7 +53,7 @@ init_node_buffer_list(node_buffer_list_t * nb, node_buffer_elem_t *head, void *x
 
 #ifdef UNIVERSAL_PARSER
 static node_buffer_t *
-rb_node_buffer_new(rb_parser_config_t *config)
+rb_node_buffer_new(const rb_parser_config_t *config)
 #else
 static node_buffer_t *
 rb_node_buffer_new(void)
@@ -318,7 +318,7 @@ rb_ast_delete_node(rb_ast_t *ast, NODE *n)
 
 #ifdef UNIVERSAL_PARSER
 rb_ast_t *
-rb_ast_new(rb_parser_config_t *config)
+rb_ast_new(const rb_parser_config_t *config)
 {
     node_buffer_t *nb = rb_node_buffer_new(config);
     return config->ast_new((VALUE)nb);
diff --git a/node.h b/node.h
index d8d104975a..009d39b856 100644
--- a/node.h
+++ b/node.h
@@ -43,14 +43,14 @@ struct node_buffer_struct {
     // Array, whose entry is array
     VALUE tokens;
 #ifdef UNIVERSAL_PARSER
-    rb_parser_config_t *config;
+    const rb_parser_config_t *config;
 #endif
 };
 
 RUBY_SYMBOL_EXPORT_BEGIN
 
 #ifdef UNIVERSAL_PARSER
-rb_ast_t *rb_ast_new(rb_parser_config_t *config);
+rb_ast_t *rb_ast_new(const rb_parser_config_t *config);
 #else
 rb_ast_t *rb_ast_new(void);
 #endif
diff --git a/parse.y b/parse.y
index 339efb3297..7cb92b88e3 100644
--- a/parse.y
+++ b/parse.y
@@ -611,7 +611,7 @@ struct parser_params {
     struct lex_context ctxt;
 
 #ifdef UNIVERSAL_PARSER
-    rb_parser_config_t *config;
+    const rb_parser_config_t *config;
 #endif
     /* compile_option */
     signed int frozen_string_literal:2; /* -1: not specified, 0: false, 1: true */
@@ -15989,7 +15989,7 @@ rb_reserved_word(const char *str, unsigned int len)
 
 #ifdef UNIVERSAL_PARSER
 rb_parser_t *
-rb_ruby_parser_allocate(rb_parser_config_t *config)
+rb_ruby_parser_allocate(const rb_parser_config_t *config)
 {
     /* parser_initialize expects fields to be set to 0 */
     rb_parser_t *p = (rb_parser_t *)config->calloc(1, sizeof(rb_parser_t));
@@ -15998,7 +15998,7 @@ rb_ruby_parser_allocate(rb_parser_config_t *config)
 }
 
 rb_parser_t *
-rb_ruby_parser_new(rb_parser_config_t *config)
+rb_ruby_parser_new(const rb_parser_config_t *config)
 {
     /* parser_initialize expects fields to be set to 0 */
     rb_parser_t *p = rb_ruby_parser_allocate(config);
diff --git a/ruby_parser.c b/ruby_parser.c
index a76a8231f5..d932b0f7be 100644
--- a/ruby_parser.c
+++ b/ruby_parser.c
@@ -484,7 +484,7 @@ extern VALUE rb_eArgError;
 extern VALUE rb_mRubyVMFrozenCore;
 VALUE rb_node_case_when_optimizable_literal(const NODE *const node);
 
-rb_parser_config_t rb_global_parser_config = (rb_parser_config_t) {
+static const rb_parser_config_t rb_global_parser_config = {
     .malloc = ruby_xmalloc,
     .calloc = ruby_xcalloc,
     .realloc = ruby_xrealloc,
diff --git a/rubyparser.h b/rubyparser.h
index 974a03992c..2bd93bf0b2 100644
--- a/rubyparser.h
+++ b/rubyparser.h
@@ -1439,8 +1439,8 @@ void rb_ruby_parser_free(void *ptr);
 rb_ast_t* rb_ruby_parser_compile_string(rb_parser_t *p, const char *f, VALUE s, int line);
 
 #ifdef UNIVERSAL_PARSER
-rb_parser_t *rb_ruby_parser_allocate(rb_parser_config_t *config);
-rb_parser_t *rb_ruby_parser_new(rb_parser_config_t *config);
+rb_parser_t *rb_ruby_parser_allocate(const rb_parser_config_t *config);
+rb_parser_t *rb_ruby_parser_new(const rb_parser_config_t *config);
 #endif
 
 long rb_parser_string_length(rb_parser_string_t *str);