diff --git a/mgraph440/pixelbase.cpp b/mgraph440/pixelbase.cpp
index 2d13ad30..a02a3f63 100644
--- a/mgraph440/pixelbase.cpp
+++ b/mgraph440/pixelbase.cpp
@@ -79,10 +79,14 @@ PixelRefVector PixelBase::pixelateLine( Line l, int scalefactor ) const
          else {
             // Special case: exactly diagonal step (should only require one step):
             // (Should actually never happen) (Doesn't: checked with RFH)
-            a.x += 1;
-            pixel_list.push_back( PixelRef(a.x,parity * a.y) );
-            a.y += 1;
-            pixel_list.push_back( PixelRef(a.x,parity * a.y) );
+            if (a.x < b.x) {
+               a.x += 1;
+               pixel_list.push_back( PixelRef(a.x,parity * a.y) );
+            }
+            if (a.y < b.y) {
+               a.y += 1;
+               pixel_list.push_back( PixelRef(a.x,parity * a.y) );
+            }
          }
       }
    }
diff --git a/salalib/spacepix.cpp b/salalib/spacepix.cpp
index 2f45857b..3294eed2 100644
--- a/salalib/spacepix.cpp
+++ b/salalib/spacepix.cpp
@@ -128,10 +128,14 @@ PixelRefVector PixelBase::pixelateLine(Line l, int scalefactor) const {
             } else {
                 // Special case: exactly diagonal step (should only require one step):
                 // (Should actually never happen) (Doesn't: checked with RFH)
-                a.x += 1;
-                pixel_list.push_back(PixelRef(a.x, parity * a.y));
-                a.y += 1;
-                pixel_list.push_back(PixelRef(a.x, parity * a.y));
+                if (a.x < b.x) {
+                    a.x += 1;
+                    pixel_list.push_back(PixelRef(a.x, parity * a.y));
+                }
+                if (a.y < b.y) {
+                    a.y += 1;
+                    pixel_list.push_back(PixelRef(a.x, parity * a.y));
+                }
             }
         }
     }