diff --git a/src/buffer.inl.hh b/src/buffer.inl.hh
index 9cfa2d0f..5375d993 100644
--- a/src/buffer.inl.hh
+++ b/src/buffer.inl.hh
@@ -52,6 +52,9 @@ inline ByteCount Buffer::offset(ByteCoord c) const
 
 inline bool Buffer::is_valid(ByteCoord c) const
 {
+    if (c.line < 0 or c.column < 0)
+        return false;
+
     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);