diff --git a/array.c b/array.c
index c0f6dd8cb6..76a3a6279d 100644
--- a/array.c
+++ b/array.c
@@ -1839,13 +1839,12 @@ ary_join_1(VALUE obj, VALUE ary, VALUE sep, long i, VALUE result, int *first)
 	    rb_str_buf_append(result, sep);
 
 	val = RARRAY_PTR(ary)[i];
-	switch (TYPE(val)) {
-	  case T_STRING:
+	if (RB_TYPE_P(val, T_STRING)) {
 	  str_join:
 	    rb_str_buf_append(result, val);
 	    *first = FALSE;
-	    break;
-	  case T_ARRAY:
+	}
+	else if (RB_TYPE_P(val, T_ARRAY)) {
 	    obj = val;
 	  ary_join:
 	    if (val == ary) {
@@ -1860,8 +1859,8 @@ ary_join_1(VALUE obj, VALUE ary, VALUE sep, long i, VALUE result, int *first)
 		args[3] = (VALUE)first;
 		rb_exec_recursive(recursive_join, obj, (VALUE)args);
 	    }
-	    break;
-	  default:
+	}
+	else {
 	    tmp = rb_check_string_type(val);
 	    if (!NIL_P(tmp)) {
 		val = tmp;
diff --git a/eval.c b/eval.c
index 958daa8752..79f4a0add7 100644
--- a/eval.c
+++ b/eval.c
@@ -34,6 +34,10 @@ VALUE rb_eSysStackError;
 #include "eval_error.c"
 #include "eval_jump.c"
 
+#define CLASS_OR_MODULE_P(obj) \
+    (!SPECIAL_CONST_P(obj) && \
+     (BUILTIN_TYPE(obj) == T_CLASS || BUILTIN_TYPE(obj) == T_MODULE))
+
 /* Initializes the Ruby VM and builtin libraries.
  * @retval 0 if succeeded.
  * @retval non-zero an error occured.
@@ -402,13 +406,17 @@ rb_mod_s_constants(int argc, VALUE *argv, VALUE mod)
 void
 rb_frozen_class_p(VALUE klass)
 {
-    const char *desc = "something(?!)";
-
+    if (SPECIAL_CONST_P(klass)) {
+      noclass:
+	Check_Type(klass, T_CLASS);
+    }
     if (OBJ_FROZEN(klass)) {
+	const char *desc;
+
 	if (FL_TEST(klass, FL_SINGLETON))
 	    desc = "object";
 	else {
-	    switch (TYPE(klass)) {
+	    switch (BUILTIN_TYPE(klass)) {
 	      case T_MODULE:
 	      case T_ICLASS:
 		desc = "module";
@@ -416,6 +424,8 @@ rb_frozen_class_p(VALUE klass)
 	      case T_CLASS:
 		desc = "class";
 		break;
+	      default:
+		goto noclass;
 	    }
 	}
 	rb_error_frozen(desc);
@@ -953,13 +963,8 @@ rb_frame_pop(void)
 static VALUE
 rb_mod_append_features(VALUE module, VALUE include)
 {
-    switch (TYPE(include)) {
-      case T_CLASS:
-      case T_MODULE:
-	break;
-      default:
+    if (!CLASS_OR_MODULE_P(include)) {
 	Check_Type(include, T_CLASS);
-	break;
     }
     rb_include_module(include, module);
 
@@ -1006,13 +1011,8 @@ rb_mod_include(int argc, VALUE *argv, VALUE module)
 static VALUE
 rb_mod_prepend_features(VALUE module, VALUE prepend)
 {
-    switch (TYPE(prepend)) {
-      case T_CLASS:
-      case T_MODULE:
-	break;
-      default:
+    if (!CLASS_OR_MODULE_P(prepend)) {
 	Check_Type(prepend, T_CLASS);
-	break;
     }
     rb_prepend_module(prepend, module);
 
diff --git a/string.c b/string.c
index 8bbd8a4c41..8b85739e70 100644
--- a/string.c
+++ b/string.c
@@ -8152,24 +8152,18 @@ rb_to_id(VALUE name)
 {
     VALUE tmp;
 
-    switch (TYPE(name)) {
-      default:
-	tmp = rb_check_string_type(name);
-	if (NIL_P(tmp)) {
-	    tmp = rb_inspect(name);
-	    rb_raise(rb_eTypeError, "%s is not a symbol",
-		     RSTRING_PTR(tmp));
-	}
-	name = tmp;
-	/* fall through */
-      case T_STRING:
-	name = rb_str_intern(name);
-	/* fall through */
-      case T_SYMBOL:
+    if (SYMBOL_P(name)) {
 	return SYM2ID(name);
     }
-
-    UNREACHABLE;
+    if (!RB_TYPE_P(name, T_STRING)) {
+	tmp = rb_check_string_type(name);
+	if (NIL_P(tmp)) {
+	    rb_raise(rb_eTypeError, "%+"PRIsVALUE" is not a symbol",
+		     name);
+	}
+	name = tmp;
+    }
+    return rb_intern_str(name);
 }
 
 /*