diff --git a/src/buffer.cc b/src/buffer.cc
index 932b5532..93360b74 100644
--- a/src/buffer.cc
+++ b/src/buffer.cc
@@ -446,4 +446,11 @@ void Buffer::notify_saved()
     }
 }
 
+bool Buffer::is_valid(const BufferCoord& c) const
+{
+   return (c.line < line_count() and c.column < m_lines[c.line].length()) or
+          (c.line == line_count() - 1 and c.column == m_lines.back().length()) or
+          (c.line == line_count() and c.column == 0);
+}
+
 }
diff --git a/src/buffer.hh b/src/buffer.hh
index b1482294..bca30078 100644
--- a/src/buffer.hh
+++ b/src/buffer.hh
@@ -123,6 +123,8 @@ public:
     String         string(const BufferIterator& begin,
                           const BufferIterator& end) const;
 
+    bool is_valid(const BufferCoord& c) const;
+
     BufferIterator begin() const;
     BufferIterator end() const;
     ByteCount      character_count() const;
diff --git a/src/buffer_iterator.inl.hh b/src/buffer_iterator.inl.hh
index e5b7c95a..ac455482 100644
--- a/src/buffer_iterator.inl.hh
+++ b/src/buffer_iterator.inl.hh
@@ -20,12 +20,7 @@ inline const Buffer& BufferIterator::buffer() const
 
 inline bool BufferIterator::is_valid() const
 {
-    return m_buffer and
-           ((line() < m_buffer->line_count() and
-             column() < m_buffer->m_lines[line()].length()) or
-            ((line() == m_buffer->line_count() and column() == 0)) or
-             (line() == m_buffer->line_count() - 1 and
-              column() == m_buffer->m_lines.back().length()));
+    return m_buffer and m_buffer->is_valid(m_coord);
 }
 
 inline void BufferIterator::clamp(bool avoid_eol)