diff --git a/include/Range.h b/include/Range.h
index 8f8834e..f66bcf0 100644
--- a/include/Range.h
+++ b/include/Range.h
@@ -10,7 +10,7 @@ public:
 
   inline Range16 operator-(Range16 a);
   inline Range16 operator+(Range16 a);
-  inline Range16 operator-();
+  inline Range16 &operator-();
 
   inline bool operator==(Range16 a);
   inline bool operator!=(Range16 a);
diff --git a/src/Range.cpp b/src/Range.cpp
index 3e3661e..af23906 100644
--- a/src/Range.cpp
+++ b/src/Range.cpp
@@ -28,7 +28,7 @@ Range16::Range16(short s) {
 Range16 Range16::operator-(Range16 a) { this->range - a.range; };
 Range16 Range16::operator+(Range16 a) { this->range + a.range; };
 
-Range16 Range16::operator-() { -this->range; }
+Range16 &Range16::operator-() { -this->range; }
 
 bool Range16::operator==(Range16 a) { this->range == a.range; }
 bool Range16::operator!=(Range16 a) { return (this->range != a.range); }