diff --git a/src/tuple.cpp b/src/tuple.cpp
index 769c3ea..e63fec0 100644
--- a/src/tuple.cpp
+++ b/src/tuple.cpp
@@ -29,6 +29,7 @@
 /* ------------------------------------------------------------------------- */
 
 #include <cmath>
+#include <cstdio>
 
 #include "tuple.h"
 
@@ -56,7 +57,7 @@ bool Tuple::operator==(const Tuple &an_other) const
 
 /* ------------------------------------------------------------------------- */
 
-Tuple &Tuple::operator+(const Tuple &an_other)
+const Tuple &Tuple::operator+(const Tuple &an_other)
 {
     m_x += an_other.m_x;
     m_y += an_other.m_y;
@@ -68,7 +69,7 @@ Tuple &Tuple::operator+(const Tuple &an_other)
 
 /* ------------------------------------------------------------------------- */
 
-Tuple &Tuple::operator-(const Tuple &an_other)
+const Tuple &Tuple::operator-(const Tuple &an_other)
 {
     m_x -= an_other.m_x;
     m_y -= an_other.m_y;
@@ -80,6 +81,18 @@ Tuple &Tuple::operator-(const Tuple &an_other)
 
 /* ------------------------------------------------------------------------- */
 
+const Tuple &Tuple::operator-(void)
+{
+    m_x = -m_x;
+    m_y = -m_y;
+    m_z = -m_z;
+    m_w = -m_w;
+
+    return *this;
+}
+
+/* ------------------------------------------------------------------------- */
+
 Tuple Tuple::Point(float an_x, float an_y, float an_z)
 {
     return Tuple(an_x, an_y, an_z, kRaytracerTuplePoint);
diff --git a/src/tuple.h b/src/tuple.h
index 8cea465..fc7aced 100644
--- a/src/tuple.h
+++ b/src/tuple.h
@@ -41,8 +41,9 @@ namespace Raytracer
         Tuple(float an_x, float an_y, float an_z, float an_w);
 
         bool operator==(const Tuple &an_other) const;
-        Tuple &operator+(const Tuple &an_other);
-        Tuple &operator-(const Tuple &an_other);
+        const Tuple &operator+(const Tuple &an_other);
+        const Tuple &operator-(const Tuple &an_other);
+        const Tuple &operator-(void);
 
         static Tuple Point(float an_x, float an_y, float an_z);
         static Tuple Vector(float an_x, float an_y, float an_z);
diff --git a/tests/chapitre01_tuples.cpp b/tests/chapitre01_tuples.cpp
index 9b429ea..0afe901 100644
--- a/tests/chapitre01_tuples.cpp
+++ b/tests/chapitre01_tuples.cpp
@@ -120,3 +120,22 @@ TEST_CASE("Subtracting two vectors", "[Tuple][Operations]")
 
   REQUIRE((v1 - v2) == Tuple::Vector(-2, -4, -6));
 }
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("Subtracting a vector from the zero vector", "[Tuple][Operations]")
+{
+  Tuple zero = Tuple::Vector(0, 0, 0);
+  Tuple v = Tuple::Vector(1, -2, 3);
+
+  REQUIRE((zero - v) == Tuple::Vector(-1, 2, -3));
+}
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("Negative a tuple", "[Tuple][Operations]")
+{
+  Tuple a(1, -2, 3, -4);
+
+  REQUIRE(-a == Tuple(-1, 2, -3, 4));
+}