diff --git a/defs/keywords b/defs/keywords
index fc30ec2d15..a1b1f4f60f 100644
--- a/defs/keywords
+++ b/defs/keywords
@@ -2,7 +2,7 @@
 struct kwtable {short name, id[2], state;};
 const struct kwtable *rb_reserved_word(const char *, unsigned int);
 #ifndef RIPPER
-static const struct kwtable *reserved_word(/*!ANSI{*/const char *, unsigned int/*}!ANSI*/);
+static const struct kwtable *reserved_word(register const char *str, register size_t len);
 #define rb_reserved_word(str, len) reserved_word(str, len)
 %}
 
diff --git a/defs/lex.c.src b/defs/lex.c.src
index fc30ec2d15..a1b1f4f60f 100644
--- a/defs/lex.c.src
+++ b/defs/lex.c.src
@@ -2,7 +2,7 @@
 struct kwtable {short name, id[2], state;};
 const struct kwtable *rb_reserved_word(const char *, unsigned int);
 #ifndef RIPPER
-static const struct kwtable *reserved_word(/*!ANSI{*/const char *, unsigned int/*}!ANSI*/);
+static const struct kwtable *reserved_word(register const char *str, register size_t len);
 #define rb_reserved_word(str, len) reserved_word(str, len)
 %}
 
diff --git a/enc/jis/props.h.blt b/enc/jis/props.h.blt
index 54aa94f8bc..508a084449 100644
--- a/enc/jis/props.h.blt
+++ b/enc/jis/props.h.blt
@@ -69,7 +69,7 @@ struct enc_property {
     unsigned char ctype;
 };
 
-static const struct enc_property *onig_jis_property(/*const char *str, unsigned int len*/);
+static const struct enc_property *onig_jis_property(register const char *str, register size_t len);
 #line 43 "enc/jis/props.kwd"
 struct enc_property;
 
@@ -82,7 +82,7 @@ struct enc_property;
 
 #ifndef GPERF_DOWNCASE
 #define GPERF_DOWNCASE 1
-static unsigned char gperf_downcase[256] =
+static const unsigned char gperf_downcase[256] =
   {
       0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,
      15,  16,  17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,
diff --git a/enc/jis/props.kwd b/enc/jis/props.kwd
index 659cf0aff4..9606828459 100644
--- a/enc/jis/props.kwd
+++ b/enc/jis/props.kwd
@@ -37,7 +37,7 @@ struct enc_property {
     unsigned char ctype;
 };
 
-static const struct enc_property *onig_jis_property(/*!ANSI{*/const char *str, unsigned int len/*}!ANSI*/);
+static const struct enc_property *onig_jis_property(register const char *str, register size_t len);
 %}
 
 struct enc_property;
diff --git a/enc/jis/props.src b/enc/jis/props.src
index 659cf0aff4..9606828459 100644
--- a/enc/jis/props.src
+++ b/enc/jis/props.src
@@ -37,7 +37,7 @@ struct enc_property {
     unsigned char ctype;
 };
 
-static const struct enc_property *onig_jis_property(/*!ANSI{*/const char *str, unsigned int len/*}!ANSI*/);
+static const struct enc_property *onig_jis_property(register const char *str, register size_t len);
 %}
 
 struct enc_property;
diff --git a/enc/unicode/14.0.0/name2ctype.h b/enc/unicode/14.0.0/name2ctype.h
index 99a3eeca19..61c16bafc2 100644
--- a/enc/unicode/14.0.0/name2ctype.h
+++ b/enc/unicode/14.0.0/name2ctype.h
@@ -40642,11 +40642,7 @@ struct uniname2ctype_struct {
 };
 #define uniname2ctype_offset(str) offsetof(struct uniname2ctype_pool_t, uniname2ctype_pool_##str)
 
-static const struct uniname2ctype_struct *uniname2ctype_p(
-#if !(1+0) /* if ANSI, old style not to conflict with generated prototype */
-    const char *, unsigned int
-#endif
-);
+static const struct uniname2ctype_struct *uniname2ctype_p(register const char *str, register size_t len);
 
 #ifndef USE_UNICODE_PROPERTIES
 #define TOTAL_KEYWORDS 15
diff --git a/ext/date/zonetab.h b/ext/date/zonetab.h
index 39a435db16..7ced9e0308 100644
--- a/ext/date/zonetab.h
+++ b/ext/date/zonetab.h
@@ -36,7 +36,7 @@ struct zone {
     int name;
     int offset;
 };
-static const struct zone *zonetab();
+static const struct zone *zonetab(register const char *str, register size_t len);
 #line 9 "zonetab.list"
 struct zone;
 
diff --git a/ext/date/zonetab.list b/ext/date/zonetab.list
index d2f902d2d5..748aec1d8a 100644
--- a/ext/date/zonetab.list
+++ b/ext/date/zonetab.list
@@ -3,7 +3,7 @@ struct zone {
     int name;
     int offset;
 };
-static const struct zone *zonetab();
+static const struct zone *zonetab(register const char *str, register size_t len);
 %}
 
 struct zone;
diff --git a/lex.c.blt b/lex.c.blt
index 92a4793b00..85727ed00f 100644
--- a/lex.c.blt
+++ b/lex.c.blt
@@ -34,7 +34,7 @@
 struct kwtable {short name, id[2], state;};
 const struct kwtable *rb_reserved_word(const char *, unsigned int);
 #ifndef RIPPER
-static const struct kwtable *reserved_word(/*const char *, unsigned int*/);
+static const struct kwtable *reserved_word(register const char *str, register size_t len);
 #define rb_reserved_word(str, len) reserved_word(str, len)
 #line 9 "defs/keywords"
 struct kwtable;
diff --git a/tool/enc-unicode.rb b/tool/enc-unicode.rb
index 60d3fca753..6f2576cc37 100755
--- a/tool/enc-unicode.rb
+++ b/tool/enc-unicode.rb
@@ -465,11 +465,7 @@ struct uniname2ctype_struct {
 };
 #define uniname2ctype_offset(str) offsetof(struct uniname2ctype_pool_t, uniname2ctype_pool_##str)
 
-static const struct uniname2ctype_struct *uniname2ctype_p(
-#if !(/*ANSI*/+0) /* if ANSI, old style not to conflict with generated prototype */
-    const char *, unsigned int
-#endif
-);
+static const struct uniname2ctype_struct *uniname2ctype_p(register const char *str, register size_t len);
 %}
 struct uniname2ctype_struct;
 %%