diff --git a/glitch.gui/cv_fractal.hpp b/glitch.gui/cv_fractal.hpp
index 56c3e6f..5353925 100644
--- a/glitch.gui/cv_fractal.hpp
+++ b/glitch.gui/cv_fractal.hpp
@@ -37,7 +37,7 @@ namespace cv_fract {
                 std::cerr << "Error invalid iterations\n";
         }
 
-        void setZoom(double z) {
+        void setZoom(const double &z) {
             zoom_ = z;
         }