diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4f38620..068a71a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -95,7 +95,7 @@ add_executable(unit_tests
         sources/Models/Components.hpp
         sources/CPU/Instruction.hpp
         sources/Exceptions/DebuggableError.hpp
-)
+        tests/CPU/Math/testOthersMath.cpp)
 
 # include criterion & coverage
 target_link_libraries(unit_tests criterion -lgcov)
diff --git a/sources/CPU/Instructions/MathematicalOperations.cpp b/sources/CPU/Instructions/MathematicalOperations.cpp
index 2b16056..54fa345 100644
--- a/sources/CPU/Instructions/MathematicalOperations.cpp
+++ b/sources/CPU/Instructions/MathematicalOperations.cpp
@@ -93,7 +93,7 @@ namespace ComSquare::CPU
 
 	int CPU::DEX(uint24_t, AddressingMode)
 	{
-		unsigned negativeMask = this->_registers.p.x_b ? UINT8_MAX : UINT16_MAX;
+		unsigned negativeMask = this->_registers.p.x_b ? 0x80 : 0x8000;
 
 		this->_registers.x--;
 		if (this->_registers.p.x_b)
@@ -105,7 +105,7 @@ namespace ComSquare::CPU
 
 	int CPU::DEY(uint24_t, AddressingMode)
 	{
-		unsigned negativeMask = this->_registers.p.x_b ? UINT8_MAX : UINT16_MAX;
+		unsigned negativeMask = this->_registers.p.x_b ? 0x80 : 0x8000;
 
 		this->_registers.y--;
 		if (this->_registers.p.x_b)
diff --git a/tests/CPU/Math/testOthersMath.cpp b/tests/CPU/Math/testOthersMath.cpp
new file mode 100644
index 0000000..1d8ed65
--- /dev/null
+++ b/tests/CPU/Math/testOthersMath.cpp
@@ -0,0 +1,119 @@
+//
+// Created by anonymus-raccoon on 4/3/20.
+//
+
+#include <criterion/criterion.h>
+#include <bitset>
+#include "../../tests.hpp"
+#include "../../../sources/SNES.hpp"
+using namespace ComSquare;
+
+Test(DEX, simple)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.x = 0x57;
+	snes.cpu->DEX(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.x, 0x56, "The x index value should be 0x56 but it was 0x%x.", snes.cpu->_registers.x);
+	cr_assert_eq(snes.cpu->_registers.p.n, false, "The negative flags should not be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEX, overflowEmul)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.x = 0;
+	snes.cpu->DEX(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.x, 0xFF, "The x index value should be 0xFF but it was 0x%x.", snes.cpu->_registers.x);
+	cr_assert_eq(snes.cpu->_registers.p.n, true, "The negative flags should be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEX, fakeOverflowNonEmul)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = false;
+	snes.cpu->_registers.x = 0xFF00;
+	snes.cpu->DEX(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.x, 0xFEFF, "The x index value should be 0xFEFF but it was 0x%x.", snes.cpu->_registers.x);
+	cr_assert_eq(snes.cpu->_registers.p.n, true, "The negative flags should be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEX, nonNegative)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.x = 0x80;
+	snes.cpu->DEX(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.x, 0x7F, "The x index value should be 0x7F but it was 0x%x.", snes.cpu->_registers.x);
+	cr_assert_eq(snes.cpu->_registers.p.n, false, "The negative flags should not be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEX, zero)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.x = 1;
+	snes.cpu->DEX(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.x, 0, "The x index value should be 0 but it was 0x%x.", snes.cpu->_registers.x);
+	cr_assert_eq(snes.cpu->_registers.p.n, false, "The negative flags should not be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, true, "The zero flags should be set.");
+}
+
+Test(DEY, simple)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.y = 0x57;
+	snes.cpu->DEY(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.y, 0x56, "The x index value should be 0x56 but it was 0x%x.", snes.cpu->_registers.y);
+	cr_assert_eq(snes.cpu->_registers.p.n, false, "The negative flags should not be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEY, overflowEmul)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.y = 0;
+	snes.cpu->DEY(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.y, 0xFF, "The x index value should be 0xFF but it was 0x%x.", snes.cpu->_registers.y);
+	cr_assert_eq(snes.cpu->_registers.p.n, true, "The negative flags should be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEY, fakeOverflowNonEmul)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = false;
+	snes.cpu->_registers.y = 0xFF00;
+	snes.cpu->DEY(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.y, 0xFEFF, "The x index value should be 0xFEFF but it was 0x%x.", snes.cpu->_registers.y);
+	cr_assert_eq(snes.cpu->_registers.p.n, true, "The negative flags should be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEY, nonNegative)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.y = 0x80;
+	snes.cpu->DEY(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.y, 0x7F, "The x index value should be 0x7F but it was 0x%x.", snes.cpu->_registers.y);
+	cr_assert_eq(snes.cpu->_registers.p.n, false, "The negative flags should not be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, false, "The zero flags should not be set.");
+}
+
+Test(DEY, zero)
+{
+	Init()
+	snes.cpu->_registers.p.x_b = true;
+	snes.cpu->_registers.y = 1;
+	snes.cpu->DEY(0x0, ComSquare::CPU::AddressingMode::Implied);
+	cr_assert_eq(snes.cpu->_registers.y, 0, "The x index value should be 0 but it was 0x%x.", snes.cpu->_registers.y);
+	cr_assert_eq(snes.cpu->_registers.p.n, false, "The negative flags should not be set.");
+	cr_assert_eq(snes.cpu->_registers.p.z, true, "The zero flags should be set.");
+}
\ No newline at end of file