diff --git a/src/cpu.rs b/src/cpu.rs
index 661080d..500414f 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -108,7 +108,7 @@ impl From<u32> for Instruction {
             }
             fmt => {
                 let imediate = (value & (1 << 28)) != 0;
-                let s = (value & 1 << 27) != 0;
+                let s = (value & 1 << 29) != 0;
                 const MASK: u32 = 0b1111;
                 let opcode = (value >> 24) & MASK;
                 let rd = Reg(((value >> 20) & MASK) as u8);