diff --git a/src/cpu/thumb/format3.zig b/src/cpu/thumb/format3.zig
index 7939113..a40e627 100644
--- a/src/cpu/thumb/format3.zig
+++ b/src/cpu/thumb/format3.zig
@@ -28,6 +28,7 @@ pub fn format3(comptime op: u2, comptime rd: u3) InstrFn {
                     cpu.cpsr.v.write(((left ^ result) & (~offset ^ result)) >> 31 & 1 == 1);
                 },
                 0b10 => {
+                    // ADD
                     const left = cpu.r[rd];
 
                     var result: u32 = undefined;
@@ -40,7 +41,15 @@ pub fn format3(comptime op: u2, comptime rd: u3) InstrFn {
                     cpu.cpsr.v.write(((left ^ result) & (offset ^ result)) >> 31 & 1 == 1);
                 },
                 0b11 => {
-                    std.debug.panic("TODO: Implement sub R{}, #0x{X:0>2}", .{ rd, offset });
+                    // SUB
+                    const left = cpu.r[rd];
+                    const result = left -% offset;
+                    cpu.r[rd] = result;
+
+                    cpu.cpsr.n.write(result >> 31 & 1 == 1);
+                    cpu.cpsr.z.write(result == 0);
+                    cpu.cpsr.c.write(offset <= left);
+                    cpu.cpsr.v.write(((left ^ result) & (~offset ^ result)) >> 31 & 1 == 1);
                 },
             }
         }