diff --git a/c/class_resolver.c b/c/class_resolver.c
index 2a5acff..f32adc7 100644
--- a/c/class_resolver.c
+++ b/c/class_resolver.c
@@ -389,7 +389,7 @@ struct method_entry class_resolver_lookup_method_from_interfacemethodref_index(i
                                                                                struct class_entry * origin_class_entry)
 {
   struct constant * interfacemethodref_constant = &origin_class_entry->class_file->constant_pool[interfacemethodref_index - 1];
-  assert(interfacemethodref_constant->tag == CONSTANT_InterfaceMethodref);
+  assert(interfacemethodref_constant->tag == CONSTANT_InterfaceMethodref || interfacemethodref_constant->tag == CONSTANT_Methodref);
   struct constant * nameandtype_constant = &origin_class_entry->class_file->constant_pool[interfacemethodref_constant->interfacemethodref.name_and_type_index - 1];
   assert(nameandtype_constant->tag == CONSTANT_NameAndType);
   struct constant * method_name_constant = &origin_class_entry->class_file->constant_pool[nameandtype_constant->nameandtype.name_index - 1];
diff --git a/c/execute.c b/c/execute.c
index f4b54e9..cac7f4a 100644
--- a/c/execute.c
+++ b/c/execute.c
@@ -1157,15 +1157,37 @@ void op_invokestatic(struct vm * vm, uint32_t index)
   vm_static_method_call(vm, method_entry->class_entry, method_entry->method_info);
 }
 
+#include "debug.h"
+
 void op_invokevirtual(struct vm * vm, uint32_t index)
 {
-  struct method_entry * method_entry =
-    class_resolver_lookup_method_from_methodref_index(vm->class_hash_table.length,
-                                                      vm->class_hash_table.entry,
-                                                      index,
-                                                      vm->current_frame->class_entry);
+  struct class_entry * origin_class_entry = vm->current_frame->class_entry;
 
-  vm_special_method_call(vm, method_entry->class_entry, method_entry->method_info);
+  struct constant * interfacemethodref_constant = &origin_class_entry->class_file->constant_pool[index - 1];
+  assert(interfacemethodref_constant->tag == CONSTANT_Methodref);
+  struct constant * nameandtype_constant = &origin_class_entry->class_file->constant_pool[interfacemethodref_constant->interfacemethodref.name_and_type_index - 1];
+  assert(nameandtype_constant->tag == CONSTANT_NameAndType);
+  struct constant * method_name_constant = &origin_class_entry->class_file->constant_pool[nameandtype_constant->nameandtype.name_index - 1];
+  assert(method_name_constant->tag == CONSTANT_Utf8);
+  struct constant * method_descriptor_constant = &origin_class_entry->class_file->constant_pool[nameandtype_constant->nameandtype.descriptor_index - 1];
+  assert(method_descriptor_constant->tag == CONSTANT_Utf8);
+
+  uint8_t return_type;
+  int nargs = descriptor_nargs(method_descriptor_constant, &return_type);
+  (void)return_type;
+
+  int32_t * objectref = (int32_t *)operand_stack_peek_u32(vm->current_frame, nargs + 1);
+  assert(objectref != nullptr);
+  struct class_entry * class_entry = (struct class_entry *)objectref[0];
+
+  struct method_entry method_entry =
+    class_resolver_lookup_method_from_interfacemethodref_index(vm->class_hash_table.length,
+                                                               vm->class_hash_table.entry,
+                                                               index,
+                                                               class_entry,
+                                                               vm->current_frame->class_entry);
+
+  vm_special_method_call(vm, method_entry.class_entry, method_entry.method_info);
 }
 
 void op_ior(struct vm * vm)
diff --git a/c/frame.c b/c/frame.c
index b79d3b0..b033308 100644
--- a/c/frame.c
+++ b/c/frame.c
@@ -48,7 +48,7 @@ int find_constantvalue_name_index(struct class_file * class_file)
   return 0;
 }
 
-static int descriptor_nargs(struct constant * descriptor_constant, uint8_t * return_type)
+int descriptor_nargs(struct constant * descriptor_constant, uint8_t * return_type)
 {
   assert(descriptor_constant->tag == CONSTANT_Utf8);
   assert(descriptor_constant->utf8.length >= 2);
diff --git a/c/frame.h b/c/frame.h
index 74fa9c1..7eeb09d 100644
--- a/c/frame.h
+++ b/c/frame.h
@@ -164,3 +164,4 @@ void vm_start(int class_hash_table_length,
               struct hash_table_entry * class_hash_table,
               const uint8_t * main_class,
               int main_class_length);
+int descriptor_nargs(struct constant * descriptor_constant, uint8_t * return_type);
diff --git a/java/lang/String.java b/java/lang/String.java
index 4a781d4..82b7cd2 100644
--- a/java/lang/String.java
+++ b/java/lang/String.java
@@ -19,8 +19,8 @@ public class String {
         return this.value;
     }
 
-    public static String valueOf(Object obj) {
-        return (obj == null) ? "null" : obj.toString();
+    public String toString() {
+        return this;
     }
 
     public static String valueOf(boolean b) {
@@ -42,4 +42,8 @@ public class String {
     public static String valueOf(double d) {
         return Double.toString(d);
     }
+
+    public static String valueOf(Object obj) {
+        return (obj == null) ? "null" : obj.toString();
+    }
 }