diff --git a/array.c b/array.c
index 9ea4c05c52..2e57572284 100644
--- a/array.c
+++ b/array.c
@@ -642,13 +642,13 @@ rb_assoc_new(VALUE car, VALUE cdr)
 static VALUE
 to_ary(VALUE ary)
 {
-    return rb_convert_type(ary, T_ARRAY, "Array", "to_ary");
+    return rb_convert_type_with_id(ary, T_ARRAY, "Array", idTo_ary);
 }
 
 VALUE
 rb_check_array_type(VALUE ary)
 {
-    return rb_check_convert_type(ary, T_ARRAY, "Array", "to_ary");
+    return rb_check_convert_type_with_id(ary, T_ARRAY, "Array", idTo_ary);
 }
 
 /*
@@ -2012,7 +2012,7 @@ ary_join_1(VALUE obj, VALUE ary, VALUE sep, long i, VALUE result, int *first)
 		val = tmp;
 		goto str_join;
 	    }
-	    tmp = rb_check_convert_type(val, T_ARRAY, "Array", "to_ary");
+	    tmp = rb_check_convert_type_with_id(val, T_ARRAY, "Array", idTo_ary);
 	    if (!NIL_P(tmp)) {
 		obj = val;
 		val = tmp;
diff --git a/compile.c b/compile.c
index a2a80c919a..a448b2120b 100644
--- a/compile.c
+++ b/compile.c
@@ -6598,7 +6598,7 @@ register_label(rb_iseq_t *iseq, struct st_table *labels_table, VALUE obj)
 {
     LABEL *label = 0;
     st_data_t tmp;
-    obj = rb_convert_type(obj, T_SYMBOL, "Symbol", "to_sym");
+    obj = rb_convert_type_with_id(obj, T_SYMBOL, "Symbol", idTo_sym);
 
     if (st_lookup(labels_table, obj, &tmp) == 0) {
 	label = NEW_LABEL(0);
@@ -6651,8 +6651,8 @@ iseq_build_from_ary_exception(rb_iseq_t *iseq, struct st_table *labels_table,
 	LABEL *lstart, *lend, *lcont;
 	unsigned int sp;
 
-	v = rb_convert_type(RARRAY_AREF(exception, i), T_ARRAY,
-					 "Array", "to_ary");
+	v = rb_convert_type_with_id(RARRAY_AREF(exception, i), T_ARRAY,
+					 "Array", idTo_ary);
 	if (RARRAY_LEN(v) != 6) {
 	    rb_raise(rb_eSyntaxError, "wrong exception entry");
 	}
@@ -6840,7 +6840,7 @@ iseq_build_from_ary_body(rb_iseq_t *iseq, LINK_ANCHOR *const anchor,
 			}
 			break;
 		      case TS_GENTRY:
-			op = rb_convert_type(op, T_SYMBOL, "Symbol", "to_sym");
+			op = rb_convert_type_with_id(op, T_SYMBOL, "Symbol", idTo_sym);
 			argv[j] = (VALUE)rb_global_entry(SYM2ID(op));
 			break;
 		      case TS_IC:
@@ -6856,8 +6856,8 @@ iseq_build_from_ary_body(rb_iseq_t *iseq, LINK_ANCHOR *const anchor,
 			argv[j] = Qfalse;
 			break;
 		      case TS_ID:
-			argv[j] = rb_convert_type(op, T_SYMBOL,
-						  "Symbol", "to_sym");
+			argv[j] = rb_convert_type_with_id(op, T_SYMBOL,
+						  "Symbol", idTo_sym);
 			break;
 		      case TS_CDHASH:
 			{
@@ -6865,7 +6865,7 @@ iseq_build_from_ary_body(rb_iseq_t *iseq, LINK_ANCHOR *const anchor,
 			    VALUE map = rb_hash_new();
 
 			    rb_hash_tbl_raw(map)->type = &cdhash_type;
-			    op = rb_convert_type(op, T_ARRAY, "Array", "to_ary");
+			    op = rb_convert_type_with_id(op, T_ARRAY, "Array", idTo_ary);
 			    for (i=0; i<RARRAY_LEN(op); i+=2) {
 				VALUE key = RARRAY_AREF(op, i);
 				VALUE sym = RARRAY_AREF(op, i+1);
@@ -6907,8 +6907,8 @@ iseq_build_from_ary_body(rb_iseq_t *iseq, LINK_ANCHOR *const anchor,
     return iseq_setup(iseq, anchor);
 }
 
-#define CHECK_ARRAY(v)   rb_convert_type((v), T_ARRAY, "Array", "to_ary")
-#define CHECK_SYMBOL(v)  rb_convert_type((v), T_SYMBOL, "Symbol", "to_sym")
+#define CHECK_ARRAY(v)   rb_convert_type_with_id((v), T_ARRAY, "Array", idTo_ary)
+#define CHECK_SYMBOL(v)  rb_convert_type_with_id((v), T_SYMBOL, "Symbol", idTo_sym)
 
 static int
 int_param(int *dst, VALUE param, VALUE sym)
diff --git a/file.c b/file.c
index b234910d5d..49015b5ae4 100644
--- a/file.c
+++ b/file.c
@@ -23,6 +23,7 @@
 #include <CoreFoundation/CFString.h>
 #endif
 
+#include "id.h"
 #include "internal.h"
 #include "ruby/io.h"
 #include "ruby/util.h"
@@ -1014,7 +1015,7 @@ rb_stat(VALUE file, struct stat *st)
 {
     VALUE tmp;
 
-    tmp = rb_check_convert_type(file, T_FILE, "IO", "to_io");
+    tmp = rb_check_convert_type_with_id(file, T_FILE, "IO", idTo_io);
     if (!NIL_P(tmp)) {
 	rb_io_t *fptr;
 
@@ -1033,7 +1034,7 @@ w32_io_info(VALUE *file, BY_HANDLE_FILE_INFORMATION *st)
     VALUE tmp;
     HANDLE f, ret = 0;
 
-    tmp = rb_check_convert_type(*file, T_FILE, "IO", "to_io");
+    tmp = rb_check_convert_type_with_id(*file, T_FILE, "IO", idTo_io);
     if (!NIL_P(tmp)) {
 	rb_io_t *fptr;
 
diff --git a/hash.c b/hash.c
index 61ca381ac7..3176bc7a24 100644
--- a/hash.c
+++ b/hash.c
@@ -711,13 +711,13 @@ rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
 static VALUE
 to_hash(VALUE hash)
 {
-    return rb_convert_type(hash, T_HASH, "Hash", "to_hash");
+    return rb_convert_type_with_id(hash, T_HASH, "Hash", idTo_hash);
 }
 
 VALUE
 rb_check_hash_type(VALUE hash)
 {
-    return rb_check_convert_type(hash, T_HASH, "Hash", "to_hash");
+    return rb_check_convert_type_with_id(hash, T_HASH, "Hash", idTo_hash);
 }
 
 /*
@@ -1027,7 +1027,7 @@ rb_hash_set_default_proc(VALUE hash, VALUE proc)
 	SET_DEFAULT(hash, proc);
 	return proc;
     }
-    b = rb_check_convert_type(proc, T_DATA, "Proc", "to_proc");
+    b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
     if (NIL_P(b) || !rb_obj_is_proc(b)) {
 	rb_raise(rb_eTypeError,
 		 "wrong default_proc type %s (expected Proc)",
diff --git a/internal.h b/internal.h
index ad977cbbcc..62b2664ebb 100644
--- a/internal.h
+++ b/internal.h
@@ -1428,6 +1428,8 @@ double rb_num_to_dbl(VALUE val);
 VALUE rb_obj_dig(int argc, VALUE *argv, VALUE self, VALUE notfound);
 VALUE rb_immutable_obj_clone(int, VALUE *, VALUE);
 VALUE rb_obj_not_equal(VALUE obj1, VALUE obj2);
+VALUE rb_convert_type_with_id(VALUE,int,const char*,ID);
+VALUE rb_check_convert_type_with_id(VALUE,int,const char*,ID);
 
 struct RBasicRaw {
     VALUE flags;
diff --git a/io.c b/io.c
index 19c588497a..3482602326 100644
--- a/io.c
+++ b/io.c
@@ -655,13 +655,13 @@ rb_io_get_fptr(VALUE io)
 VALUE
 rb_io_get_io(VALUE io)
 {
-    return rb_convert_type(io, T_FILE, "IO", "to_io");
+    return rb_convert_type_with_id(io, T_FILE, "IO", idTo_io);
 }
 
 VALUE
 rb_io_check_io(VALUE io)
 {
-    return rb_check_convert_type(io, T_FILE, "IO", "to_io");
+    return rb_check_convert_type_with_id(io, T_FILE, "IO", idTo_io);
 }
 
 VALUE
@@ -9938,7 +9938,7 @@ open_key_args(int argc, VALUE *argv, VALUE opt, struct foreach_arg *arg)
 	VALUE args;
 	long n;
 
-	v = rb_convert_type(v, T_ARRAY, "Array", "to_ary");
+	v = rb_convert_type_with_id(v, T_ARRAY, "Array", idTo_ary);
 	n = RARRAY_LEN(v) + 1;
 #if SIZEOF_LONG > SIZEOF_INT
 	if (n > INT_MAX) {
diff --git a/iseq.c b/iseq.c
index 81edd37c47..bfdbeadfa9 100644
--- a/iseq.c
+++ b/iseq.c
@@ -503,10 +503,10 @@ rb_iseq_load_iseq(VALUE fname)
     return NULL;
 }
 
-#define CHECK_ARRAY(v)   rb_convert_type((v), T_ARRAY, "Array", "to_ary")
-#define CHECK_HASH(v)    rb_convert_type((v), T_HASH, "Hash", "to_hash")
-#define CHECK_STRING(v)  rb_convert_type((v), T_STRING, "String", "to_str")
-#define CHECK_SYMBOL(v)  rb_convert_type((v), T_SYMBOL, "Symbol", "to_sym")
+#define CHECK_ARRAY(v)   rb_convert_type_with_id((v), T_ARRAY, "Array", idTo_ary)
+#define CHECK_HASH(v)    rb_convert_type_with_id((v), T_HASH, "Hash", idTo_hash)
+#define CHECK_STRING(v)  rb_convert_type_with_id((v), T_STRING, "String", idTo_str)
+#define CHECK_SYMBOL(v)  rb_convert_type_with_id((v), T_SYMBOL, "Symbol", idTo_sym)
 static inline VALUE CHECK_INTEGER(VALUE v) {(void)NUM2LONG(v); return v;}
 
 static enum iseq_type
diff --git a/object.c b/object.c
index 5e74359145..afeb1dc3e1 100644
--- a/object.c
+++ b/object.c
@@ -2660,28 +2660,12 @@ static const struct conv_method_tbl {
 #define IMPLICIT_CONVERSIONS 7
 
 static VALUE
-convert_type(VALUE val, const char *tname, const char *method, int raise)
+convert_type_with_id(VALUE val, const char *tname, ID method, int raise, int index)
 {
-    ID m = 0;
-    int i = numberof(conv_method_names);
-    VALUE r;
-    static const char prefix[] = "to_";
-
-    if (strncmp(prefix, method, sizeof(prefix)-1) == 0) {
-	const char *const meth = &method[sizeof(prefix)-1];
-	for (i=0; i < numberof(conv_method_names); i++) {
-	    if (conv_method_names[i].method[0] == meth[0] &&
-		strcmp(conv_method_names[i].method, meth) == 0) {
-		m = conv_method_names[i].id;
-		break;
-	    }
-	}
-    }
-    if (!m) m = rb_intern(method);
-    r = rb_check_funcall(val, m, 0, 0);
+    VALUE r = rb_check_funcall(val, method, 0, 0);
     if (r == Qundef) {
 	if (raise) {
-	    const char *msg = i < IMPLICIT_CONVERSIONS ?
+	    const char *msg = index < IMPLICIT_CONVERSIONS ?
 		"no implicit conversion of" : "can't convert";
 	    const char *cname = NIL_P(val) ? "nil" :
 		val == Qtrue ? "true" :
@@ -2698,6 +2682,27 @@ convert_type(VALUE val, const char *tname, const char *method, int raise)
     return r;
 }
 
+static VALUE
+convert_type(VALUE val, const char *tname, const char *method, int raise)
+{
+    ID m = 0;
+    int i = numberof(conv_method_names);
+    static const char prefix[] = "to_";
+
+    if (strncmp(prefix, method, sizeof(prefix)-1) == 0) {
+	const char *const meth = &method[sizeof(prefix)-1];
+	for (i=0; i < numberof(conv_method_names); i++) {
+	    if (conv_method_names[i].method[0] == meth[0] &&
+		strcmp(conv_method_names[i].method, meth) == 0) {
+		m = conv_method_names[i].id;
+		break;
+	    }
+	}
+    }
+    if (!m) m = rb_intern(method);
+    return convert_type_with_id(val, tname, m, raise, i);
+}
+
 NORETURN(static void conversion_mismatch(VALUE, const char *, const char *, VALUE));
 static void
 conversion_mismatch(VALUE val, const char *tname, const char *method, VALUE result)
@@ -2721,6 +2726,19 @@ rb_convert_type(VALUE val, int type, const char *tname, const char *method)
     return v;
 }
 
+VALUE
+rb_convert_type_with_id(VALUE val, int type, const char *tname, ID method)
+{
+    VALUE v;
+
+    if (TYPE(val) == type) return val;
+    v = convert_type_with_id(val, tname, method, TRUE, 0);
+    if (TYPE(v) != type) {
+	conversion_mismatch(val, tname, RSTRING_PTR(rb_id2str(method)), v);
+    }
+    return v;
+}
+
 VALUE
 rb_check_convert_type(VALUE val, int type, const char *tname, const char *method)
 {
@@ -2736,6 +2754,21 @@ rb_check_convert_type(VALUE val, int type, const char *tname, const char *method
     return v;
 }
 
+VALUE
+rb_check_convert_type_with_id(VALUE val, int type, const char *tname, ID method)
+{
+    VALUE v;
+
+    /* always convert T_DATA */
+    if (TYPE(val) == type && type != T_DATA) return val;
+    v = convert_type_with_id(val, tname, method, FALSE, 0);
+    if (NIL_P(v)) return Qnil;
+    if (TYPE(v) != type) {
+	conversion_mismatch(val, tname, RSTRING_PTR(rb_id2str(method)), v);
+    }
+    return v;
+}
+
 
 static VALUE
 rb_to_integer(VALUE val, const char *method)
@@ -3175,7 +3208,7 @@ rb_String(VALUE val)
 {
     VALUE tmp = rb_check_string_type(val);
     if (NIL_P(tmp))
-	tmp = rb_convert_type(val, T_STRING, "String", "to_s");
+	tmp = rb_convert_type_with_id(val, T_STRING, "String", idTo_s);
     return tmp;
 }
 
@@ -3205,7 +3238,7 @@ rb_Array(VALUE val)
     VALUE tmp = rb_check_array_type(val);
 
     if (NIL_P(tmp)) {
-	tmp = rb_check_convert_type(val, T_ARRAY, "Array", "to_a");
+	tmp = rb_check_convert_type_with_id(val, T_ARRAY, "Array", idTo_a);
 	if (NIL_P(tmp)) {
 	    return rb_ary_new3(1, val);
 	}
diff --git a/process.c b/process.c
index 67f51db847..324d112e0b 100644
--- a/process.c
+++ b/process.c
@@ -1486,7 +1486,7 @@ check_exec_redirect_fd(VALUE v, int iskey)
         else
             goto wrong;
     }
-    else if (!NIL_P(tmp = rb_check_convert_type(v, T_FILE, "IO", "to_io"))) {
+    else if (!NIL_P(tmp = rb_check_convert_type_with_id(v, T_FILE, "IO", idTo_io))) {
         rb_io_t *fptr;
         GetOpenFile(tmp, fptr);
         if (fptr->tied_io_for_writing)
@@ -2397,7 +2397,7 @@ rb_execarg_parent_start1(VALUE execarg_obj)
         }
         else {
             envtbl = rb_const_get(rb_cObject, id_ENV);
-            envtbl = rb_convert_type(envtbl, T_HASH, "Hash", "to_hash");
+            envtbl = rb_convert_type_with_id(envtbl, T_HASH, "Hash", idTo_hash);
         }
         hide_obj(envtbl);
         if (envopts != Qfalse) {
diff --git a/rational.c b/rational.c
index bd32399e79..ce95facda0 100644
--- a/rational.c
+++ b/rational.c
@@ -6,6 +6,7 @@
 */
 
 #include "internal.h"
+#include "id.h"
 #include <math.h>
 #include <float.h>
 
@@ -2610,7 +2611,7 @@ nurat_s_convert(int argc, VALUE *argv, VALUE klass)
 
     if (argc == 1) {
 	if (!(k_numeric_p(a1) && k_integer_p(a1)))
-	    return rb_convert_type(a1, T_RATIONAL, "Rational", "to_r");
+	    return rb_convert_type_with_id(a1, T_RATIONAL, "Rational", idTo_r);
     }
     else {
 	if ((k_numeric_p(a1) && k_numeric_p(a2)) &&
diff --git a/string.c b/string.c
index 89e08d2cc2..df3f8fd3cd 100644
--- a/string.c
+++ b/string.c
@@ -1341,7 +1341,7 @@ rb_str_memsize(VALUE str)
 VALUE
 rb_str_to_str(VALUE str)
 {
-    return rb_convert_type(str, T_STRING, "String", "to_str");
+    return rb_convert_type_with_id(str, T_STRING, "String", idTo_str);
 }
 
 static inline void str_discard(VALUE str);
@@ -2225,7 +2225,7 @@ rb_str_fill_terminator(VALUE str, const int newminlen)
 VALUE
 rb_check_string_type(VALUE str)
 {
-    str = rb_check_convert_type(str, T_STRING, "String", "to_str");
+    str = rb_check_convert_type_with_id(str, T_STRING, "String", idTo_str);
     return str;
 }
 
diff --git a/thread.c b/thread.c
index 4d954c76de..da834974bd 100644
--- a/thread.c
+++ b/thread.c
@@ -1875,7 +1875,7 @@ rb_thread_s_handle_interrupt(VALUE self, VALUE mask_arg)
     }
 
     mask = 0;
-    mask_arg = rb_convert_type(mask_arg, T_HASH, "Hash", "to_hash");
+    mask_arg = rb_convert_type_with_id(mask_arg, T_HASH, "Hash", idTo_hash);
     rb_hash_foreach(mask_arg, handle_interrupt_arg_check_i, (VALUE)&mask);
     if (!mask) {
 	return rb_yield(Qnil);
diff --git a/vm.c b/vm.c
index 4810321d6f..d90cb2f472 100644
--- a/vm.c
+++ b/vm.c
@@ -2736,7 +2736,7 @@ core_hash_merge_kwd(int argc, VALUE *argv)
     rb_check_arity(argc, 1, 2);
     hash = argv[0];
     kw = argv[argc-1];
-    kw = rb_convert_type(kw, T_HASH, "Hash", "to_hash");
+    kw = rb_convert_type_with_id(kw, T_HASH, "Hash", idTo_hash);
     if (argc < 2) hash = kw;
     rb_hash_foreach(kw, argc < 2 ? kwcheck_i : kwmerge_i, hash);
     return hash;
diff --git a/vm_args.c b/vm_args.c
index 3bf56788b1..ae27d27d8c 100644
--- a/vm_args.c
+++ b/vm_args.c
@@ -777,7 +777,7 @@ vm_to_proc(VALUE proc)
 {
     if (UNLIKELY(!rb_obj_is_proc(proc))) {
 	VALUE b;
-	b = rb_check_convert_type(proc, T_DATA, "Proc", "to_proc");
+	b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
 
 	if (NIL_P(b) || !rb_obj_is_proc(b)) {
 	    rb_raise(rb_eTypeError,
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index a6f2943ecd..bb483d2d2c 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -2991,8 +2991,8 @@ static VALUE
 vm_concat_array(VALUE ary1, VALUE ary2st)
 {
     const VALUE ary2 = ary2st;
-    VALUE tmp1 = rb_check_convert_type(ary1, T_ARRAY, "Array", "to_a");
-    VALUE tmp2 = rb_check_convert_type(ary2, T_ARRAY, "Array", "to_a");
+    VALUE tmp1 = rb_check_convert_type_with_id(ary1, T_ARRAY, "Array", idTo_a);
+    VALUE tmp2 = rb_check_convert_type_with_id(ary2, T_ARRAY, "Array", idTo_a);
 
     if (NIL_P(tmp1)) {
 	tmp1 = rb_ary_new3(1, ary1);
@@ -3011,7 +3011,7 @@ vm_concat_array(VALUE ary1, VALUE ary2st)
 static VALUE
 vm_splat_array(VALUE flag, VALUE ary)
 {
-    VALUE tmp = rb_check_convert_type(ary, T_ARRAY, "Array", "to_a");
+    VALUE tmp = rb_check_convert_type_with_id(ary, T_ARRAY, "Array", idTo_a);
     if (NIL_P(tmp)) {
 	return rb_ary_new3(1, ary);
     }
diff --git a/vm_trace.c b/vm_trace.c
index decb2c32e4..2f78284805 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -683,7 +683,7 @@ static rb_event_flag_t
 symbol2event_flag(VALUE v)
 {
     ID id;
-    VALUE sym = rb_convert_type(v, T_SYMBOL, "Symbol", "to_sym");
+    VALUE sym = rb_convert_type_with_id(v, T_SYMBOL, "Symbol", idTo_sym);
     const rb_event_flag_t RUBY_EVENT_A_CALL =
 	RUBY_EVENT_CALL | RUBY_EVENT_B_CALL | RUBY_EVENT_C_CALL;
     const rb_event_flag_t RUBY_EVENT_A_RETURN =