diff --git a/src/core/GapBuffer.cc b/src/core/GapBuffer.cc
index 7c55ed9..0d97caf 100644
--- a/src/core/GapBuffer.cc
+++ b/src/core/GapBuffer.cc
@@ -46,19 +46,34 @@ void GapBuffer::compact()
 /**
  * Insert code_point into the gap buffer at position position.
  *
- * @param position Position in the gap buffer to insert the code point at.
- *   Must be <= size.
+ * @param insert_cursor Cursor in the gap buffer to insert the code point at.
  * @param code_point The code point to insert.
  */
-void GapBuffer::insert(size_t position, uint32_t code_point)
+void GapBuffer::insert(Cursor & insert_cursor, uint32_t code_point)
 {
-    if (position > m_size)
-        return;
+    size_t position = insert_cursor.iterator().offset();
     check_grow();
     move_gap(position);
     size_t size = Encoding::encode(code_point, m_encoding, &m_buffer[m_gap_position]);
     m_gap_position += size;
     m_size += size;
+
+    /* Now adjust any cursors that were >= position. */
+    for (auto cursor : m_cursors)
+    {
+        if (cursor->iterator().offset() >= position)
+        {
+            cursor->iterator().set_offset(cursor->iterator().offset() + size);
+            if (cursor->line() == insert_cursor.line())
+            {
+                cursor->calculate_column();
+            }
+            if (code_point == '\n')
+            {
+                cursor->set_line(cursor->line() + 1u);
+            }
+        }
+    }
 }
 
 /**
diff --git a/src/core/GapBuffer.h b/src/core/GapBuffer.h
index 0100b89..1158ddf 100644
--- a/src/core/GapBuffer.h
+++ b/src/core/GapBuffer.h
@@ -46,6 +46,8 @@ public:
         {
             return m_offset < other.m_offset;
         }
+        size_t offset() { return m_offset; }
+        void set_offset(size_t new_offset) { m_offset = new_offset; }
 
     protected:
         GapBuffer * m_gap_buffer;
@@ -78,6 +80,9 @@ public:
         bool valid() const { return m_iterator.valid(); }
         size_t line() const { return m_line; }
         size_t column() const { return m_column; }
+        Iterator & iterator() { return m_iterator; }
+        void set_line(size_t line) { m_line = line; }
+        void calculate_column();
 
     protected:
         Iterator m_iterator;
@@ -85,7 +90,6 @@ public:
         size_t m_column;
 
         void init_column();
-        void calculate_column();
         void forward_to_column(size_t target_column);
     };
 
@@ -110,7 +114,7 @@ public:
     }
     size_t gap_size() const { return m_buffer_size - m_size; }
     void compact();
-    void insert(size_t position, uint32_t code_point);
+    void insert(Cursor & insert_cursor, uint32_t code_point);
 
 protected:
     uint8_t * m_buffer;