diff --git a/src/grt/src/cugr/src/GridGraph.cpp b/src/grt/src/cugr/src/GridGraph.cpp
index f24fe59c22..c85a99113e 100644
--- a/src/grt/src/cugr/src/GridGraph.cpp
+++ b/src/grt/src/cugr/src/GridGraph.cpp
@@ -250,6 +250,9 @@ GridGraph::GridGraph(const Design* design,
 IntervalT GridGraph::rangeSearchGridlines(const int dimension,
                                           const IntervalT& loc_interval) const
 {
+  if (dimension < 0 || dimension > 1) {
+    return {0, 0};
+  }
   IntervalT range;
   range.Set(lower_bound(gridlines_[dimension].begin(),
                         gridlines_[dimension].end(),
@@ -270,13 +273,28 @@ IntervalT GridGraph::rangeSearchGridlines(const int dimension,
 IntervalT GridGraph::rangeSearchRows(const int dimension,
                                      const IntervalT& loc_interval) const
 {
+  if (dimension < 0 || dimension > 1) {
+    return {0, 0};
+  }
+
+  // 1. Critical Empty Check: If the grid doesn't exist, exit early
+  if (gridlines_[dimension].empty()) {
+    return {0, 0};
+  }
+
   const auto& lineRange = rangeSearchGridlines(dimension, loc_interval);
-  return {gridlines_[dimension][lineRange.low()] == loc_interval.low()
-              ? lineRange.low()
-              : std::max(lineRange.low() - 1, 0),
-          gridlines_[dimension][lineRange.high()] == loc_interval.high()
-              ? lineRange.high() - 1
-              : std::min(lineRange.high(), getSize(dimension) - 1)};
+
+  // 2. BOUNDARY SHIELD: Safely clamp to array boundaries
+  const int max_idx = (int) gridlines_[dimension].size() - 1;
+  const int l = std::min(lineRange.low(), max_idx);
+  const int h = std::min(lineRange.high(), max_idx);
+
+  // 3. Robust Return: Ensure we never return a negative index for either bound
+  return {
+      gridlines_[dimension][l] == loc_interval.low() ? l : std::max(l - 1, 0),
+      gridlines_[dimension][h] == loc_interval.high()
+          ? std::max(0, h - 1)
+          : std::min(h, getSize(dimension) - 1)};
 }
 
 BoxT GridGraph::getCellBox(PointT point) const
@@ -908,4 +926,4 @@ void GridGraph::write(const std::string& heatmap_file) const
   fout.close();
 }
 
-}  // namespace grt
+}  // namespace grt
\ No newline at end of file