diff --git a/include/Athena/Global.hpp b/include/Athena/Global.hpp
index 9659c12..304f189 100644
--- a/include/Athena/Global.hpp
+++ b/include/Athena/Global.hpp
@@ -22,6 +22,12 @@
 #define S_ISLNK(m) 0
 #endif
 
+#define PRISize "Iu"
+
+#else
+
+#define PRISize "zu"
+
 #endif
 
 #ifndef AT_PRETTY_FUNCTION
diff --git a/src/Athena/FileWriter.cpp b/src/Athena/FileWriter.cpp
index d6f579a..3d916d5 100644
--- a/src/Athena/FileWriter.cpp
+++ b/src/Athena/FileWriter.cpp
@@ -59,7 +59,7 @@ void FileWriter::open(bool overwrite)
 
     if (!m_fileHandle)
     {
-        atError("Unable to open file '%s'", filename());
+        atError("Unable to open file '%s'", filename().c_str());
         setError();
         return;
     }