diff --git a/image_analysis/scale_merge/ScaleOnTheFly.cpp b/image_analysis/scale_merge/ScaleOnTheFly.cpp
index cc3a9c64..fa60a7d6 100644
--- a/image_analysis/scale_merge/ScaleOnTheFly.cpp
+++ b/image_analysis/scale_merge/ScaleOnTheFly.cpp
@@ -235,6 +235,8 @@ ScaleOnTheFlyResult ScaleOnTheFly::Scale(std::vector<Reflection> &reflections,
     }
     result.succesful = true;
 
+    problem.SetParameterLowerBound(&result.G, 0, 0.0);
+
     if (s.GetRefineB()) {
         problem.SetParameterLowerBound(&result.B, 0, s.GetMinB());
         problem.SetParameterUpperBound(&result.B, 0, s.GetMaxB());