diff --git a/apps/shared/sum_graph_controller.cpp b/apps/shared/sum_graph_controller.cpp
index 2412ded9f..b2052130c 100644
--- a/apps/shared/sum_graph_controller.cpp
+++ b/apps/shared/sum_graph_controller.cpp
@@ -157,9 +157,11 @@ SumGraphController::LegendView::LegendView(SumGraphController * controller, Inpu
   m_sum(0.0f, 0.5f, KDColorBlack, Palette::GreyMiddle),
   m_sumLayout(),
   m_legend(k_font, I18n::Message::Default, 0.0f, 0.5f, KDColorBlack, Palette::GreyMiddle),
-  m_editableZone(controller, nullptr, TextField::maxBufferSize(), TextField::maxBufferSize(), inputEventHandlerDelegate, controller, k_font, 0.0f, 0.5f, KDColorBlack, Palette::GreyMiddle),
+  m_editableZone(controller, m_textBuffer, k_editableZoneBufferSize, TextField::maxBufferSize(), inputEventHandlerDelegate, controller, k_font, 0.0f, 0.5f, KDColorBlack, Palette::GreyMiddle),
   m_sumSymbol(sumSymbol)
-{}
+{
+  m_textBuffer[0] = 0;
+}
 
 void SumGraphController::LegendView::drawRect(KDContext * ctx, KDRect rect) const {
   ctx->fillRect(bounds(), Palette::GreyMiddle);
diff --git a/apps/shared/sum_graph_controller.h b/apps/shared/sum_graph_controller.h
index 3b9871e42..77e7d8e65 100644
--- a/apps/shared/sum_graph_controller.h
+++ b/apps/shared/sum_graph_controller.h
@@ -2,6 +2,7 @@
 #define SHARED_SUM_GRAPH_CONTROLLER_H
 
 #include <escher.h>
+#include <poincare/print_float.h>
 #include "function_graph_view.h"
 #include "vertical_cursor_view.h"
 #include "simple_interactive_curve_view_controller.h"
@@ -56,6 +57,7 @@ private:
     void setEditableZone(double d);
     void setSumSymbol(Step step, double start, double end, double result, Poincare::Layout functionLayout);
   private:
+    constexpr static KDCoordinate k_editableZoneBufferSize = Poincare::PrintFloat::k_maxFloatBufferSize;
     constexpr static KDCoordinate k_legendHeight = 35;
     constexpr static const KDFont * k_font = KDFont::SmallFont;
     static KDCoordinate editableZoneWidth() { return 12*k_font->glyphSize().width(); }
@@ -70,6 +72,7 @@ private:
     Poincare::Layout m_sumLayout;
     MessageTextView m_legend;
     TextField m_editableZone;
+    char m_textBuffer[k_editableZoneBufferSize];
     CodePoint m_sumSymbol;
   };
   FunctionGraphView * m_graphView;