diff --git a/tests/test_cpu_state.cpp b/tests/test_cpu_state.cpp
index c744ebf..e5e9373 100644
--- a/tests/test_cpu_state.cpp
+++ b/tests/test_cpu_state.cpp
@@ -18,3 +18,14 @@ TEST_CASE("16-bit registers map to two 8-bit registers")
   CHECK(c.H == 0x33);
   CHECK(c.L == 0x44);
 }
+
+TEST_CASE("SI works correctly")
+{
+  Cpu_state c;
+
+
+  c.IE = 0b10000111;
+  c.IF = 0b10011100;
+
+  CHECK(c.SI() == 0b00000100);
+}