diff --git a/README.md b/README.md
index 63ca8d62..aa523ced 100644
--- a/README.md
+++ b/README.md
@@ -5709,6 +5709,14 @@ It returns -1 in case of error in decoding the UTF8 string.
 
 Return the position in the stream of the iterator 'it'.
 
+##### void string\_it\_set\_ref(string\_it\_t it, string\_t str, string\_unicode\_t u)
+
+Replace the unicode code point referenced by 'it' to the unicode code point 'u'
+in the string 'str'.
+If 'u' is 0, then it will resize the string to the size of the referenced iterator
+only keeping the unicode code points before the iterator.
+'it' shall be a valid iterator of 'str'.
+
 ##### bool string\_it\_equal\_p (const string\_it\_t it1, const string\_it\_t it2)
 
 Return true if both iterators reference the same position, false otherwise.
diff --git a/m-string.h b/m-string.h
index 0d608861..783e1c88 100644
--- a/m-string.h
+++ b/m-string.h
@@ -1863,6 +1863,56 @@ m_string_cref (m_string_it_t it)
   return &it->u;
 }
 
+/* Update the value referenced by the iterator to the given value */
+static inline void
+m_string_it_set_ref(m_string_it_t it, m_string_t s, m_string_unicode_t new_u)
+{
+  M_STR1NG_IT_CONTRACT(it);
+  M_STR1NG_CONTRACT(s);
+  M_ASSERT(s == it->string);
+  char *ptr = m_str1ng_get_cstr(s);
+  M_ASSUME( it->ptr >= ptr);
+  size_t offset = (size_t) (it->ptr - ptr);
+  // Special case if the unicode codepoint is 0
+  if (new_u == 0) {
+    // Null the string
+    m_str1ng_set_size(s, offset);
+    ptr[offset] = 0;
+    M_STR1NG_IT_CONTRACT(it);
+    M_STR1NG_CONTRACT(s);
+    return;
+  }
+  // Encode the new unicode code point & compute its size
+  char buffer[4+1];
+  m_str1ng_utf8_encode(buffer, new_u);
+  size_t new_u_size = strlen(buffer);
+  // Compute the size of the old unicode code point
+  m_str1ng_utf8_state_e state =  M_STR1NG_UTF8_STARTING;
+  m_string_unicode_t old_u = 0;
+  const char *str = it->ptr;
+  do {
+    m_str1ng_utf8_decode(*str, &state, &old_u);
+    str++;
+  } while (state != M_STR1NG_UTF8_STARTING && state != M_STR1NG_UTF8_ERROR && *str != 0);
+  M_ASSUME( str > it->ptr);
+  size_t old_u_size = (size_t) (str - it->ptr);
+  // We need to replace old_u by new_u. Both are variable length
+  size_t str_size = m_string_size(s);
+  m_str1ng_fit2size(s, str_size + new_u_size - old_u_size + 1);
+  ptr = m_str1ng_get_cstr(s); // ptr may be reallocated!
+  if (new_u_size != old_u_size) {
+    M_ASSUME( str_size+1 > (offset + old_u_size) );
+    memmove(&ptr[offset+new_u_size], &ptr[offset + old_u_size],
+            str_size+1 - offset - old_u_size);
+  }
+  memcpy(&ptr[offset], &buffer[0], new_u_size);
+  m_str1ng_set_size(s, str_size + new_u_size - old_u_size);
+  it->ptr = &ptr[offset];
+  M_STR1NG_IT_CONTRACT(it);
+  M_STR1NG_CONTRACT(s);
+  return;
+}
+
 /* Push unicode code point into string, encoding it in UTF8 */
 static inline void
 m_string_push_u (m_string_t str, m_string_unicode_t u)
@@ -2714,6 +2764,7 @@ namespace m_lib {
 #define string_it_pos m_string_it_pos
 #define string_it_get_pos m_string_it_get_pos
 #define string_previous m_string_previous
+#define string_it_set_ref m_string_it_set_ref
 
 #define STRING_CTE M_STRING_CTE
 #define STRING_DECL_INIT M_STRING_DECL_INIT
diff --git a/tests/test-mstring.c b/tests/test-mstring.c
index 9bdc4949..9158a711 100644
--- a/tests/test-mstring.c
+++ b/tests/test-mstring.c
@@ -172,6 +172,52 @@ static void test_utf8_it(void)
   assert(!string_it_equal_p(it, it2));
 
   string_clear(s);
+
+  /* Test replacing of unicode */
+  string_init(s);
+  for (string_unicode_t u = 1; u < 0x10ffff; u+=3) {
+    if (u < 0xD800U || u > 0xDFFFU) {
+      for(int c1 = 0 ; c1 <= 3; c1+=2) {
+        for(int c2 = 0 ; c2 <= 20; c2+=5) {
+          const string_unicode_t u_tab[] = { 0, 'B', 300, 45215, 0x10fffe};
+          for(int c3 = 0 ; c3 < 5; c3++) {
+            // Generate string
+            string_reset(s);
+            for(int j = 0; j < c1; j++)
+              string_push_back(s, 'A');
+            string_push_u(s, u);
+            for(int j = 0; j < c2; j++)
+              string_push_back(s, 'C');
+            // Replace iterator in string
+            string_it(it, s);
+            for(int j = 0; j < c1; j++)
+              string_next(it);
+            assert( string_get_cref(it) == u);
+            string_it_set_ref(it, s, u_tab[c3]);
+            if (u_tab[c3] != 0) {
+              assert( string_get_cref(it) == u_tab[c3]);
+            }
+            // Check constructed string
+            string_it(it, s);
+            for(int j = 0; j < c1; j++) {
+              assert( string_get_cref(it) == 'A');
+              string_next(it);
+            }
+            if (u_tab[c3] != 0) {
+              assert( *string_cref(it) == u_tab[c3]);
+              string_next(it);
+              for(int j = 0; j < c2; j++) {
+                assert( string_get_cref(it) == 'C');
+                string_next(it);
+              }
+            }
+            assert(string_end_p(it));
+          }
+        }
+      }
+    }
+  }
+  string_clear(s);
 }
 
 static void call_string_cat_vprintf(string_t s, const char format[], ...)