diff --git a/ion/src/shared/unicode/utf8_decoder.cpp b/ion/src/shared/unicode/utf8_decoder.cpp
index a91895417..c95279bb1 100644
--- a/ion/src/shared/unicode/utf8_decoder.cpp
+++ b/ion/src/shared/unicode/utf8_decoder.cpp
@@ -79,22 +79,22 @@ size_t UTF8Decoder::CodePointToChars(CodePoint c, char * buffer, size_t bufferSi
     buffer[i++] = c;
   } else if (charCount == 2) {
     buffer[i++] = 0b11000000 | (c >> 6);
-    if (bufferSize <= i) { return i; }
+    if (bufferSize <= i) { return bufferSize; }
     buffer[i++] = 0b10000000 | (c & 0b111111);
   } else if (charCount == 3) {
     buffer[i++] = 0b11100000 | (c >> 12);
-    if (bufferSize <= i) { return i; }
+    if (bufferSize <= i) { return bufferSize; }
     buffer[i++] = 0b10000000 | ((c >> 6) & 0b111111);
-    if (bufferSize <= i) { return i; }
+    if (bufferSize <= i) { return bufferSize; }
     buffer[i++] = 0b10000000 | (c & 0b111111);
   } else {
     assert(charCount == 4);
     buffer[i++] = 0b11110000 | (c >> 18);
-    if (bufferSize <= i) { return i; }
+    if (bufferSize <= i) { return bufferSize; }
     buffer[i++] = 0b10000000 | ((c >> 12) & 0b111111);
-    if (bufferSize <= i) { return i; }
+    if (bufferSize <= i) { return bufferSize; }
     buffer[i++] = 0b10000000 | ((c >> 6) & 0b111111);
-    if (bufferSize <= i) { return i; }
+    if (bufferSize <= i) { return bufferSize; }
     buffer[i++] = 0b10000000 | (c & 0b111111);
   }
   assert(i == charCount);
diff --git a/poincare/src/serialization_helper.cpp b/poincare/src/serialization_helper.cpp
index 770acec6b..7c9ec1fb9 100644
--- a/poincare/src/serialization_helper.cpp
+++ b/poincare/src/serialization_helper.cpp
@@ -184,8 +184,12 @@ int SerializationHelper::CodePoint(char * buffer, int bufferSize, class CodePoin
     }
   }
   size_t size = UTF8Decoder::CodePointToChars(c, buffer, bufferSize);
-  assert(size <= bufferSize - 1);
-  buffer[size] = 0;
+  if (size <= bufferSize - 1) {
+    buffer[size] = 0;
+  } else {
+    assert(size -1 == bufferSize - 1);
+    buffer[--size] = 0;
+  }
   return size;
 }