diff --git a/src/if_mzsch.h b/src/if_mzsch.h
index 65c5de7..7c1766e 100644
--- a/src/if_mzsch.h
+++ b/src/if_mzsch.h
@@ -7,6 +7,7 @@
 #ifdef __MINGW32__
 /* Hack to engage Cygwin-specific settings */
 # define __CYGWIN32__
+# include <stdint.h>
 #endif
 
 /* #ifdef needed for "make depend" */
@@ -20,31 +21,24 @@
 #endif
 
 #if MZSCHEME_VERSION_MAJOR >= 299
-/* macros to be compatible with 20x versions */
-# define scheme_config scheme_current_config()
-# define scheme_make_string scheme_make_byte_string
-# define scheme_make_string_output_port scheme_make_byte_string_output_port
-# define scheme_get_sized_string_output scheme_get_sized_byte_string_output
-# define scheme_write_string scheme_write_byte_string
-# define scheme_make_sized_string scheme_make_sized_byte_string
-
 # define SCHEME_STRINGP(obj) (SCHEME_BYTE_STRINGP(obj) || SCHEME_CHAR_STRINGP(obj))
-# define SCHEME_STR_VAL(obj) SCHEME_BYTE_STR_VAL(   \
-		(SCHEME_BYTE_STRINGP(obj) ? obj : scheme_char_string_to_byte_string(obj)))
-# define GUARANTEE_STRING(fname, argnum) GUARANTEE_TYPE(fname, argnum, SCHEME_STRINGP, "string")
-
-# ifdef scheme_format
-#  undef scheme_format
-# endif
-# define scheme_format scheme_format_utf8
-
-# define SCHEME_GET_BYTE_STRING(obj) (SCHEME_BYTE_STRINGP(obj) ? obj :   \
-	scheme_char_string_to_byte_string(obj))
+# define BYTE_STRING_VALUE(obj) ((char_u *)SCHEME_BYTE_STR_VAL(obj))
 #else
-# define SCHEME_GET_BYTE_STRING(obj) (obj)
+/* macros for compatibility with older versions */
+# define scheme_current_config() scheme_config
+# define scheme_make_sized_byte_string scheme_make_sized_string
+# define scheme_format_utf8 scheme_format
+# ifndef DYNAMIC_MZSCHEME
+/* for dynamic MzScheme there will be separate definitions in if_mzsch.c */
+#  define scheme_get_sized_byte_string_output scheme_get_sized_string_output
+#  define scheme_make_byte_string scheme_make_string
+#  define scheme_make_byte_string_output_port scheme_make_string_output_port
+# endif
+
 # define SCHEME_BYTE_STRLEN_VAL SCHEME_STRLEN_VAL
-# define SCHEME_BYTE_STR_VAL SCHEME_STR_VAL
+# define BYTE_STRING_VALUE(obj) ((char_u *)SCHEME_STR_VAL(obj))
 # define scheme_byte_string_to_char_string(obj) (obj)
+# define SCHEME_BYTE_STRINGP SCHEME_STRINGP
 #endif
 
 /* Precise GC macros */