diff --git a/src/zm_box.h b/src/zm_box.h
index 9b9e33bc2..22210f2f8 100644
--- a/src/zm_box.h
+++ b/src/zm_box.h
@@ -32,7 +32,7 @@
 class Box {
  public:
   Box() = default;
-  Box(Vector2 lo, Vector2 hi) : lo_(lo), hi_(hi), size_(Vector2::Range(hi, lo)) {}
+  Box(Vector2 lo, Vector2 hi) : lo_(lo), hi_(hi), size_(hi - lo) {}
 
   const Vector2 &Lo() const { return lo_; }
   const Vector2 &Hi() const { return hi_; }
diff --git a/src/zm_image.cpp b/src/zm_image.cpp
index f61974004..5fc53253f 100644
--- a/src/zm_image.cpp
+++ b/src/zm_image.cpp
@@ -2389,10 +2389,11 @@ void Image::Outline( Rgb colour, const Polygon &polygon ) {
     const Vector2 &p1 = polygon.GetVertices()[i];
     const Vector2 &p2 = polygon.GetVertices()[j];
 
-    int x1 = p1.x_;
-    int x2 = p2.x_;
-    int y1 = p1.y_;
-    int y2 = p2.y_;
+    // The last pixel we can draw is width/height - 1. Clamp to that value.
+    int x1 = ZM::clamp(p1.x_, 0, static_cast<int>(width - 1));
+    int x2 = ZM::clamp(p2.x_, 0, static_cast<int>(width - 1));
+    int y1 = ZM::clamp(p1.y_, 0, static_cast<int>(height - 1));
+    int y2 = ZM::clamp(p2.y_, 0, static_cast<int>(height - 1));
 
     double dx = x2 - x1;
     double dy = y2 - y1;
diff --git a/src/zm_vector2.h b/src/zm_vector2.h
index 0daa51d77..c7630ad36 100644
--- a/src/zm_vector2.h
+++ b/src/zm_vector2.h
@@ -37,11 +37,6 @@ class Vector2 {
     return inf;
   }
 
-  static Vector2 Range(const Vector2 &coord1, const Vector2 &coord2) {
-    Vector2 result((coord1.x_ - coord2.x_) + 1, (coord1.y_ - coord2.y_) + 1);
-    return result;
-  }
-
   bool operator==(const Vector2 &rhs) const { return (x_ == rhs.x_ && y_ == rhs.y_); }
   bool operator!=(const Vector2 &rhs) const { return (x_ != rhs.x_ || y_ != rhs.y_); }
 
diff --git a/src/zm_zone.cpp b/src/zm_zone.cpp
index 413a407c5..7a73b93ed 100644
--- a/src/zm_zone.cpp
+++ b/src/zm_zone.cpp
@@ -874,8 +874,8 @@ std::vector<Zone> Zone::Load(Monitor *monitor) {
       continue;
     }
 
-    if (polygon.Extent().Lo().x_ < 0 || polygon.Extent().Hi().x_ >= (int) monitor->Width()
-        || polygon.Extent().Lo().y_ < 0 || polygon.Extent().Hi().y_ >= (int) monitor->Height()) {
+    if (polygon.Extent().Lo().x_ < 0 || polygon.Extent().Hi().x_ > static_cast<int32>(monitor->Width())
+        || polygon.Extent().Lo().y_ < 0 || polygon.Extent().Hi().y_ > static_cast<int32>(monitor->Height())) {
       Error("Zone %d/%s for monitor %s extends outside of image dimensions, (%d,%d), (%d,%d), fixing",
             Id,
             Name,
diff --git a/tests/zm_box.cpp b/tests/zm_box.cpp
index 8141bfa54..e85056c85 100644
--- a/tests/zm_box.cpp
+++ b/tests/zm_box.cpp
@@ -34,15 +34,10 @@ TEST_CASE("Box: construct from lo and hi") {
   SECTION("basic properties") {
   REQUIRE(b.Lo() == Vector2(1, 1));
   REQUIRE(b.Hi() == Vector2(5, 5));
-  // Should be:
-  // REQUIRE(b.Size() == Vector2(4 ,4));
-  REQUIRE(b.Size() == Vector2(5, 5));
-  // Should be:
-  // REQUIRE(b.Area() == 16);
-  REQUIRE(b.Area() == 25);
-  // Should be:
-  // REQUIRE(b.Centre() == Vector2(3, 3));
-  REQUIRE(b.Centre() == Vector2(4, 4));
+
+  REQUIRE(b.Size() == Vector2(4 ,4));
+  REQUIRE(b.Area() == 16);
+  REQUIRE(b.Centre() == Vector2(3, 3));
 
   REQUIRE(b.Vertices() == std::vector<Vector2>{{1, 1}, {5, 1}, {5, 5}, {1, 5}});
   }
diff --git a/tests/zm_poly.cpp b/tests/zm_poly.cpp
index 817b5a32c..8ce775d6c 100644
--- a/tests/zm_poly.cpp
+++ b/tests/zm_poly.cpp
@@ -31,10 +31,7 @@ TEST_CASE("Polygon: construct from vertices") {
   Polygon p(vertices);
 
   REQUIRE(p.Area() == 18);
-  //REQUIRE(p.Centre() == Vector2(2, 2));
-  // Mathematically should be:
-  //REQUIRE(p.Extent().Size() == Vector2(6, 6));
-  REQUIRE(p.Extent().Size() == Vector2(7, 7));
+  REQUIRE(p.Extent().Size() == Vector2(6, 6));
 }
 
 TEST_CASE("Polygon: clipping") {
@@ -56,24 +53,19 @@ TEST_CASE("Polygon: clipping") {
   Polygon p(v);
 
   REQUIRE(p.GetVertices().size() == 11);
-  REQUIRE(p.Extent().Size() == Vector2(9, 8));
-  // should be:
-  // REQUIRE(p.Extent().Size() == Vector2(8, 7));
-  // related to Vector2::Range
+  REQUIRE(p.Extent().Size() == Vector2(8, 7));
 
   SECTION("boundary box larger than polygon") {
     Polygon c = p.GetClipped(Box({1, 0}, {11, 9}));
 
     REQUIRE(c.GetVertices().size() == 11);
-    REQUIRE(c.Extent().Size() == Vector2(9, 8));
+    REQUIRE(c.Extent().Size() == Vector2(8, 7));
   }
 
   SECTION("boundary box smaller than polygon") {
     Polygon c = p.GetClipped(Box({2, 4}, {10, 7}));
 
     REQUIRE(c.GetVertices().size() == 8);
-    REQUIRE(c.Extent().Size() == Vector2(9, 4));
-    // should be:
-    // REQUIRE(c.Extent().Size() == Vector2(8, 3));
+    REQUIRE(c.Extent().Size() == Vector2(8, 3));
   }
 }