diff --git a/include/instructions.h b/include/instructions.h
index 2373cc4..db875a3 100644
--- a/include/instructions.h
+++ b/include/instructions.h
@@ -25,6 +25,7 @@ public:
 
   void add_rm32_r32();  // 0x01
   void xor_rm32_r32();  // 0x31
+  void dec_r32();       // 0x48 ~ 0x4f
   void mov_rm32_r32();  // 0x89
   void nop();           // 0x90
   void mov_ecx_imm32(); // 0xb9
diff --git a/instructions.cpp b/instructions.cpp
index 511be6d..c023449 100644
--- a/instructions.cpp
+++ b/instructions.cpp
@@ -22,6 +22,12 @@ void Instructions::init_instructions(){
 
   this->instructions[0x01] = &Instructions::add_rm32_r32;
   this->instructions[0x31] = &Instructions::xor_rm32_r32;
+
+  for(int i = 0;i < 8;i++){
+    // 0x48 ~ 0x4f : dec_r32
+    this->instructions[0x48+i] = &Instructions::dec_r32;
+  }
+
   this->instructions[0x89] = &Instructions::mov_rm32_r32;
   this->instructions[0x90] = &Instructions::nop;
   this->instructions[0xb9] = &Instructions::mov_ecx_imm32;
@@ -146,6 +152,12 @@ void Instructions::xor_rm32_r32(){
   }
 }
 
+void Instructions::dec_r32(){
+  printf("dec_r32 called.\n");
+  uint8_t opcode = memory.read_uint8(this->eip-1);
+  this->registers[opcode - 0x48]--;
+}
+
 void Instructions::mov_rm32_r32(){
   printf("mov_rm32_r32 called.\n");
   uint32_t addr, imm32;