diff --git a/internal/parse.h b/internal/parse.h
index f70e8e75a3..0132557951 100644
--- a/internal/parse.h
+++ b/internal/parse.h
@@ -19,13 +19,5 @@ RUBY_SYMBOL_EXPORT_BEGIN
 VALUE rb_parser_set_context(VALUE, const struct rb_iseq_struct *, int);
 RUBY_SYMBOL_EXPORT_END
 void *rb_parser_load_file(VALUE parser, VALUE name);
-int rb_is_const_name(VALUE name);
-int rb_is_class_name(VALUE name);
-int rb_is_instance_name(VALUE name);
-int rb_is_local_name(VALUE name);
-PUREFUNC(int rb_is_const_sym(VALUE sym));
-PUREFUNC(int rb_is_attrset_sym(VALUE sym));
-ID rb_make_internal_id(void);
-void rb_gc_free_dsymbol(VALUE);
 
 #endif /* INTERNAL_PARSE_H */
diff --git a/internal/symbol.h b/internal/symbol.h
index 8423cb4dc8..0317f66561 100644
--- a/internal/symbol.h
+++ b/internal/symbol.h
@@ -9,21 +9,29 @@
  *             modify this file, provided that  the conditions mentioned in the
  *             file COPYING are met.  Consult the file for details.
  */
+#include "ruby/ruby.h"          /* for VALUE */
+#include "ruby/encoding.h"      /* for rb_encoding */
+#include "internal/compilers.h" /* for __has_builtin */
 
 /* symbol.c */
-#ifdef RUBY_ENCODING_H
+VALUE rb_to_symbol_type(VALUE obj);
 VALUE rb_sym_intern(const char *ptr, long len, rb_encoding *enc);
-#endif
 VALUE rb_sym_intern_ascii(const char *ptr, long len);
 VALUE rb_sym_intern_ascii_cstr(const char *ptr);
-#ifdef __GNUC__
-#define rb_sym_intern_ascii_cstr(ptr) __extension__ ( \
-{                                               \
-    (__builtin_constant_p(ptr)) ?               \
+int rb_is_const_name(VALUE name);
+int rb_is_class_name(VALUE name);
+int rb_is_instance_name(VALUE name);
+int rb_is_local_name(VALUE name);
+PUREFUNC(int rb_is_const_sym(VALUE sym));
+PUREFUNC(int rb_is_attrset_sym(VALUE sym));
+ID rb_make_internal_id(void);
+void rb_gc_free_dsymbol(VALUE);
+
+#if __has_builtin(__builtin_constant_p)
+#define rb_sym_intern_ascii_cstr(ptr) \
+    (__builtin_constant_p(ptr) ? \
         rb_sym_intern_ascii((ptr), (long)strlen(ptr)) : \
-        rb_sym_intern_ascii_cstr(ptr); \
-})
+        rb_sym_intern_ascii_cstr(ptr))
 #endif
-VALUE rb_to_symbol_type(VALUE obj);
 
 #endif /* INTERNAL_SYMBOL_H */