diff --git a/enc/unicode/10.0.0/name2ctype.h b/enc/unicode/10.0.0/name2ctype.h
index 4a1422d17a..680560707f 100644
--- a/enc/unicode/10.0.0/name2ctype.h
+++ b/enc/unicode/10.0.0/name2ctype.h
@@ -34756,9 +34756,11 @@ struct uniname2ctype_struct {
 };
 #define uniname2ctype_offset(str) offsetof(struct uniname2ctype_pool_t, uniname2ctype_pool_##str)
 
-#if !1+0
-static const struct uniname2ctype_struct *uniname2ctype_p(const char *, unsigned int);
+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
+);
 
 #ifndef USE_UNICODE_PROPERTIES
 #define TOTAL_KEYWORDS 15
diff --git a/numeric.c b/numeric.c
index c66da93b03..8f0a805c68 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3902,7 +3902,7 @@ rb_int_modulo(VALUE x, VALUE y)
  *  See Numeric#divmod.
  */
 
-VALUE
+static VALUE
 int_remainder(VALUE x, VALUE y)
 {
     if (FIXNUM_P(x)) {
diff --git a/tool/enc-unicode.rb b/tool/enc-unicode.rb
index c5c593f617..b0819c35ab 100755
--- a/tool/enc-unicode.rb
+++ b/tool/enc-unicode.rb
@@ -448,9 +448,11 @@ struct uniname2ctype_struct {
 };
 #define uniname2ctype_offset(str) offsetof(struct uniname2ctype_pool_t, uniname2ctype_pool_##str)
 
-#if !(/*ANSI*/+0)
-static const struct uniname2ctype_struct *uniname2ctype_p(const char *, unsigned int);
+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
+);
 %}
 struct uniname2ctype_struct;
 %%
diff --git a/vm_backtrace.c b/vm_backtrace.c
index 776f6d188a..8264018da0 100644
--- a/vm_backtrace.c
+++ b/vm_backtrace.c
@@ -693,7 +693,7 @@ rb_ec_backtrace_str_ary(const rb_execution_context_t *ec, long lev, long n)
     return backtrace_to_str_ary(rb_ec_backtrace_object(ec), lev, n);
 }
 
-VALUE
+static VALUE
 ec_backtrace_location_ary(const rb_execution_context_t *ec, long lev, long n)
 {
     return backtrace_to_location_ary(rb_ec_backtrace_object(ec), lev, n);