diff --git a/filetype.cc b/filetype.cc
index 9eaad6f6..40f36285 100644
--- a/filetype.cc
+++ b/filetype.cc
@@ -27,6 +27,9 @@ string simplifyString( string const & str )
   while( endPos && Utf8::isspace( str[ endPos - 1 ] ) )
     --endPos;
 
+  if( endPos <= beginPos )
+    return string();
+
   result.reserve( endPos - beginPos );
 
   while( beginPos < endPos )