diff --git a/pelican/writers.py b/pelican/writers.py
index 73f025b6..73ee4b33 100644
--- a/pelican/writers.py
+++ b/pelican/writers.py
@@ -25,7 +25,7 @@ class Writer:
         self._overridden_files = set()
 
         # See Content._link_replacer for details
-        if self.settings['RELATIVE_URLS']:
+        if "RELATIVE_URLS" in self.settings and self.settings['RELATIVE_URLS']:
             self.urljoiner = posix_join
         else:
             self.urljoiner = lambda base, url: urljoin(