diff --git a/apps/shared/sum_graph_controller.h b/apps/shared/sum_graph_controller.h
index de57d7691..3119d9577 100644
--- a/apps/shared/sum_graph_controller.h
+++ b/apps/shared/sum_graph_controller.h
@@ -57,7 +57,7 @@ private:
     void setEditableZone(double d);
     void setSumLayout(Step step, double start, double end, double result, Poincare::Layout functionLayout);
   private:
-    constexpr static KDCoordinate k_editableZoneBufferSize = Poincare::PrintFloat::k_maxFloatCharSize;
+    constexpr static size_t k_editableZoneBufferSize = Poincare::PrintFloat::k_maxFloatCharSize;
     constexpr static KDCoordinate k_legendHeight = 35;
     constexpr static const KDFont * k_font = KDFont::SmallFont;
     static KDCoordinate editableZoneWidth() { return 12*k_font->glyphSize().width(); }