diff --git a/src/scale_denominator.cpp b/src/scale_denominator.cpp
index 1ea7f7dae..993bdd709 100644
--- a/src/scale_denominator.cpp
+++ b/src/scale_denominator.cpp
@@ -34,7 +34,11 @@ static const double meters_per_degree = EARTH_CIRCUMFERENCE / 360;
 
 double scale_denominator(double map_scale, bool geographic)
 {
-    double denom = map_scale / 0.00028;
+    // Pixel size in meters.
+    // Corresponding approximate resolution is 90.71 DPI.
+    constexpr double pixel_size = 0.00028;
+
+    double denom = map_scale / pixel_size;
     if (geographic) denom *= meters_per_degree;
     return denom;
 }