diff --git a/gbso/insn.py b/gbso/insn.py
index ccee90a..440a7da 100644
--- a/gbso/insn.py
+++ b/gbso/insn.py
@@ -717,7 +717,8 @@ class ADD_SP_DD(Insn):
     def exec(self, cpu: CPU) -> None:
         sp = cpu.get_reg16(R16.SP) + self.dd
         cpu.carry = 1 if sp > 0xFFFF or sp < 0 else 0
-        cpu.set_reg16(R16.SP, sp)
+        cpu.set_reg16(R16.SP, sp & 0xFFFF)
+        cpu.cycles += 16
 
     def pretty(self) -> str:
         return f"ADD SP, {self.dd}"
@@ -730,7 +731,8 @@ class LD_HL_SP_DD(Insn):
     def exec(self, cpu: CPU) -> None:
         sp = cpu.get_reg16(R16.SP) + self.dd
         cpu.carry = 1 if sp > 0xFFFF or sp < 0 else 0
-        cpu.set_reg16(R16.HL, sp)
+        cpu.set_reg16(R16.HL, sp & 0xFFFF)
+        cpu.cycles += 12
 
     def pretty(self) -> str:
         return f"LD HL, SP + {self.dd}"
diff --git a/tests/insn/test_alu16.py b/tests/insn/test_alu16.py
index 05c4963..a762acf 100644
--- a/tests/insn/test_alu16.py
+++ b/tests/insn/test_alu16.py
@@ -43,3 +43,51 @@ def test_dec_rr(rr):
 
     assert cpu.get_reg16(rr) == 0xABCC
     assert cpu.cycles == 8
+
+
+def test_add_sp_dd():
+    cpu = CPU()
+    cpu.set_reg16(R16.SP, 0xFFFF)
+
+    ADD_SP_DD(-1).exec(cpu)
+
+    assert cpu.get_reg16(R16.SP) == 0xFFFE
+    assert cpu.carry == 0
+    assert cpu.cycles == 16
+
+    ADD_SP_DD(2).exec(cpu)
+
+    assert cpu.get_reg16(R16.SP) == 0
+    assert cpu.carry == 1
+    assert cpu.cycles == 32
+
+    ADD_SP_DD(-1).exec(cpu)
+
+    assert cpu.get_reg16(R16.SP) == 0xFFFF
+    assert cpu.carry == 1
+    assert cpu.cycles == 48
+
+
+def test_ld_hl_sp_dd():
+    cpu = CPU()
+    cpu.set_reg16(R16.SP, 0xFFFF)
+
+    LD_HL_SP_DD(1).exec(cpu)
+
+    assert cpu.get_reg16(R16.HL) == 0
+    assert cpu.carry == 1
+    assert cpu.cycles == 12
+
+    cpu.set_reg16(R16.SP, 0)
+    LD_HL_SP_DD(-1).exec(cpu)
+
+    assert cpu.get_reg16(R16.HL) == 0xFFFF
+    assert cpu.carry == 1
+    assert cpu.cycles == 24
+
+    cpu.set_reg16(R16.SP, 0xFFFF)
+    LD_HL_SP_DD(-2).exec(cpu)
+
+    assert cpu.get_reg16(R16.HL) == 0xFFFD
+    assert cpu.carry == 0
+    assert cpu.cycles == 36