diff --git a/src/cpu.zig b/src/cpu.zig
index c8de217..485452e 100644
--- a/src/cpu.zig
+++ b/src/cpu.zig
@@ -31,6 +31,7 @@ const format6 = @import("cpu/thumb/format6.zig").format6;
 const format78 = @import("cpu/thumb/format78.zig").format78;
 const format9 = @import("cpu/thumb/format9.zig").format9;
 const format10 = @import("cpu/thumb/format10.zig").format10;
+const format11 = @import("cpu/thumb/format11.zig").format11;
 const format12 = @import("cpu/thumb/format12.zig").format12;
 const format13 = @import("cpu/thumb/format13.zig").format13;
 const format14 = @import("cpu/thumb/format14.zig").format14;
@@ -486,8 +487,10 @@ fn thumbPopulate() [0x400]ThumbInstrFn {
 
                 lut[i] = format10(L, offset);
             } else if (i >> 6 & 0xF == 0b1001) {
-                // Format 11 | SP-relative load / store
-                lut[i] = thumbUndefined;
+                const L = i >> 5 & 1 == 1;
+                const rd = i >> 2 & 0x3;
+
+                lut[i] = format11(L, rd);
             } else if (i >> 6 & 0xF == 0b1010) {
                 const isSP = i >> 5 & 1 == 1;
                 const rd = i >> 2 & 0x7;
diff --git a/src/cpu/thumb/format11.zig b/src/cpu/thumb/format11.zig
new file mode 100644
index 0000000..b17783d
--- /dev/null
+++ b/src/cpu/thumb/format11.zig
@@ -0,0 +1,21 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format11(comptime L: bool, comptime rd: u3) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u16) void {
+            const offset = (opcode & 0xFF) << 2;
+            const address = cpu.r[13] + offset;
+
+            if (L) {
+                const value = bus.read32(address & 0xFFFF_FFFC);
+                cpu.r[rd] = std.math.rotr(u32, value, 8 * (address & 0x3));
+            } else {
+                bus.write32(address & 0xFFFF_FFFC, cpu.r[rd]);
+            }
+        }
+    }.inner;
+}