diff --git a/evm/src/cpu/kernel/interpreter.rs b/evm/src/cpu/kernel/interpreter.rs
index 877e24ab..8a898cb3 100644
--- a/evm/src/cpu/kernel/interpreter.rs
+++ b/evm/src/cpu/kernel/interpreter.rs
@@ -263,7 +263,7 @@ impl<'a> Interpreter<'a> {
             0x56 => self.run_jump(),                                    // "JUMP",
             0x57 => self.run_jumpi(),                                   // "JUMPI",
             0x58 => todo!(),                                            // "GETPC",
-            0x59 => todo!(),                                            // "MSIZE",
+            0x59 => self.run_msize(),                                   // "MSIZE",
             0x5a => todo!(),                                            // "GAS",
             0x5b => self.run_jumpdest(),                                // "JUMPDEST",
             0x5c => todo!(),                                            // "GET_STATE_ROOT",
@@ -511,6 +511,14 @@ impl<'a> Interpreter<'a> {
         }
     }
 
+    fn run_msize(&mut self) {
+        let num_bytes = self.memory.context_memory[self.context].segments
+            [Segment::MainMemory as usize]
+            .content
+            .len();
+        self.push(U256::from(num_bytes));
+    }
+
     fn run_jumpdest(&mut self) {
         assert!(!self.kernel_mode, "JUMPDEST is not needed in kernel code");
     }