diff --git a/apps/sequence/sequence.cpp b/apps/sequence/sequence.cpp
index 02701e9fd..0f2a359d7 100644
--- a/apps/sequence/sequence.cpp
+++ b/apps/sequence/sequence.cpp
@@ -2,6 +2,7 @@
 #include "cache_context.h"
 #include "sequence_store.h"
 #include <poincare/layout_helper.h>
+#include <poincare/serialization_helper.h>
 #include <poincare/code_point_layout.h>
 #include <poincare/vertical_offset_layout.h>
 #include <poincare/integer.h>
@@ -122,11 +123,11 @@ T Sequence::approximateToNextRank(int n, SequenceContext * sqctx) const {
   if (n < initialRank() || n < 0) {
     return NAN;
   }
-  constexpr int bufferSize = 5;
+
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
   char unknownN[bufferSize];
-  int codePointSize = UTF8Decoder::CodePointToChars(UCodePointUnknownN, unknownN, bufferSize);
-  assert(codePointSize <= bufferSize - 1);
-  unknownN[codePointSize] = 0;
+  Poincare::SerializationHelper::CodePoint(unknownN, bufferSize, UCodePointUnknownN);
+
   CacheContext<T> ctx = CacheContext<T>(sqctx);
   T un = sqctx->valueOfSequenceAtPreviousRank<T>(0, 0);
   T unm1 = sqctx->valueOfSequenceAtPreviousRank<T>(0, 1);
diff --git a/apps/shared/cartesian_function.cpp b/apps/shared/cartesian_function.cpp
index 7faa5492e..b6d304e61 100644
--- a/apps/shared/cartesian_function.cpp
+++ b/apps/shared/cartesian_function.cpp
@@ -3,6 +3,7 @@
 #include "poincare_helpers.h"
 #include <poincare/derivative.h>
 #include <poincare/integral.h>
+#include <poincare/serialization_helper.h>
 #include <escher/palette.h>
 #include <ion/unicode/utf8_decoder.h>
 #include <float.h>
@@ -104,34 +105,30 @@ double CartesianFunction::sumBetweenBounds(double start, double end, Poincare::C
 }
 
 Expression::Coordinate2D CartesianFunction::nextMinimumFrom(double start, double step, double max, Context * context) const {
-  constexpr int bufferSize = 3;
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
   char unknownX[bufferSize];
-  int codePointSize = UTF8Decoder::CodePointToChars(UCodePointUnknownX, unknownX, bufferSize);
-  assert(codePointSize <= bufferSize);
+  SerializationHelper::CodePoint(unknownX, bufferSize, UCodePointUnknownX);
   return PoincareHelpers::NextMinimum(expressionReduced(context), unknownX, start, step, max, *context);
 }
 
 Expression::Coordinate2D CartesianFunction::nextMaximumFrom(double start, double step, double max, Context * context) const {
-  constexpr int bufferSize = 3;
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
   char unknownX[bufferSize];
-  int codePointSize = UTF8Decoder::CodePointToChars(UCodePointUnknownX, unknownX, bufferSize);
-  assert(codePointSize <= bufferSize);
+  SerializationHelper::CodePoint(unknownX, bufferSize, UCodePointUnknownX);
   return PoincareHelpers::NextMaximum(expressionReduced(context), unknownX, start, step, max, *context);
 }
 
 double CartesianFunction::nextRootFrom(double start, double step, double max, Context * context) const {
-  constexpr int bufferSize = 3;
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
   char unknownX[bufferSize];
-  int codePointSize = UTF8Decoder::CodePointToChars(UCodePointUnknownX, unknownX, bufferSize);
-  assert(codePointSize <= bufferSize);
+  SerializationHelper::CodePoint(unknownX, bufferSize, UCodePointUnknownX);
   return PoincareHelpers::NextRoot(expressionReduced(context), unknownX, start, step, max, *context);
 }
 
 Expression::Coordinate2D CartesianFunction::nextIntersectionFrom(double start, double step, double max, Poincare::Context * context, Expression e) const {
-  constexpr int bufferSize = 3;
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
   char unknownX[bufferSize];
-  int codePointSize = UTF8Decoder::CodePointToChars(UCodePointUnknownX, unknownX, bufferSize);
-  assert(codePointSize <= bufferSize);
+  SerializationHelper::CodePoint(unknownX, bufferSize, UCodePointUnknownX);
   return PoincareHelpers::NextIntersection(expressionReduced(context), unknownX, start, step, max, *context, e);
 }
 
diff --git a/poincare/src/symbol.cpp b/poincare/src/symbol.cpp
index a0711dc46..1bb2f97d9 100644
--- a/poincare/src/symbol.cpp
+++ b/poincare/src/symbol.cpp
@@ -157,7 +157,7 @@ bool SymbolNode::isUnknown(CodePoint unknownSymbol) const {
 }
 
 Symbol Symbol::Builder(CodePoint name) {
-  constexpr int bufferSize = 5;
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
   char buffer[bufferSize];
   int codePointSize = UTF8Decoder::CodePointToChars(name, buffer, bufferSize);
   assert(codePointSize <= bufferSize);
diff --git a/poincare/src/trigonometry.cpp b/poincare/src/trigonometry.cpp
index 2c7403a5a..84b694c5c 100644
--- a/poincare/src/trigonometry.cpp
+++ b/poincare/src/trigonometry.cpp
@@ -8,6 +8,7 @@
 #include <poincare/power.h>
 #include <poincare/preferences.h>
 #include <poincare/rational.h>
+#include <poincare/serialization_helper.h>
 #include <poincare/sign_function.h>
 #include <poincare/subtraction.h>
 #include <poincare/symbol.h>
@@ -22,11 +23,11 @@ namespace Poincare {
 
 float Trigonometry::characteristicXRange(const Expression & e, Context & context, Preferences::AngleUnit angleUnit) {
   assert(e.numberOfChildren() == 1);
-  constexpr int size = 5;
-  char x[size];
-  int zeroIndex = UTF8Decoder::CodePointToChars(UCodePointUnknownX, x, size);
-  assert(zeroIndex <= size - 1);
-  x[zeroIndex] = 0;
+
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
+  char x[bufferSize];
+  SerializationHelper::CodePoint(x, bufferSize, UCodePointUnknownX);
+
   int d = e.childAtIndex(0).polynomialDegree(context, x);
   if (d < 0 || d > 1) {
     // child(0) is not linear so we cannot easily find an interesting range
diff --git a/poincare/test/user_variable.cpp b/poincare/test/user_variable.cpp
index 562aeae43..f22fdd477 100644
--- a/poincare/test/user_variable.cpp
+++ b/poincare/test/user_variable.cpp
@@ -2,6 +2,7 @@
 #include <ion.h>
 #include <assert.h>
 #include <apps/shared/global_context.h>
+#include <poincare/serialization_helper.h>
 #include "helper.h"
 
 using namespace Poincare;
@@ -156,11 +157,11 @@ QUIZ_CASE(poincare_user_variable_functions_with_context) {
   // f : x→ x^2
   assert_simplify("x^2→f(x)");
   // Approximate f(?-2) with ? = 5
-  constexpr int bufferSize = 5;
+
+  constexpr int bufferSize = CodePoint::MaxCodePointCharLength + 1;
   char x[bufferSize];
-  int codePointSize = UTF8Decoder::CodePointToChars(UCodePointUnknownX, x, bufferSize);
-  quiz_assert(codePointSize <= bufferSize - 1);
-  x[codePointSize] = 0;
+  Poincare::SerializationHelper::CodePoint(x, bufferSize, UCodePointUnknownX);
+
   assert_parsed_expression_approximates_with_value_for_symbol(Function::Builder("f", 1, Subtraction::Builder(Symbol::Builder(UCodePointUnknownX), Rational::Builder(2))), x, 5.0, 9.0);
   // Approximate f(?-1)+f(?+1) with ? = 3
   assert_parsed_expression_approximates_with_value_for_symbol(Addition::Builder(Function::Builder("f", 1, Subtraction::Builder(Symbol::Builder(UCodePointUnknownX), Rational::Builder(1))), Function::Builder("f", 1, Addition::Builder(Symbol::Builder(UCodePointUnknownX), Rational::Builder(1)))), x, 3.0, 20.0);