diff --git a/src/support/filename.C b/src/support/filename.C
index 330df317a1..8762717ec1 100644
--- a/src/support/filename.C
+++ b/src/support/filename.C
@@ -41,7 +41,7 @@ FileName::~FileName()
 FileName::FileName(string const & abs_filename)
 	: name_(abs_filename)
 {
-	BOOST_ASSERT(absolutePath(name_));
+	BOOST_ASSERT(empty() || absolutePath(name_));
 	BOOST_ASSERT(!contains(name_, '\\'));
 }