diff --git a/internal/ceres/visibility.cc b/internal/ceres/visibility.cc
index 5dceeb8..fd41648 100644
--- a/internal/ceres/visibility.cc
+++ b/internal/ceres/visibility.cc
@@ -136,8 +136,9 @@
     CHECK_NE(camera1, camera2);
 
     const int count = it->second;
+    // Static cast necessary for Windows.
     const double weight = static_cast<double>(count) /
-        (sqrt(visibility[camera1].size() * visibility[camera2].size()));
+        (sqrt(static_cast<double>(visibility[camera1].size() * visibility[camera2].size())));
     graph->AddEdge(camera1, camera2, weight);
   }