diff --git a/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/__init__.py b/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/__init__.py
index dc6c1dd2fb..98f5e3c4be 100644
--- a/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/__init__.py
+++ b/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/__init__.py
@@ -67,7 +67,7 @@ def pretty_filename(filename):
     try:
         a = os.path.abspath(filename)
         r = os.path.relpath(filename)
-        return a if len(a) < len(r) else r
+        return a if '..' in r else r
     except ValueError:
         return filename
 
diff --git a/pyuavcan/pyuavcan/dsdl/common.py b/pyuavcan/pyuavcan/dsdl/common.py
index 216cce6b1b..4cbeb61577 100644
--- a/pyuavcan/pyuavcan/dsdl/common.py
+++ b/pyuavcan/pyuavcan/dsdl/common.py
@@ -30,4 +30,4 @@ def pretty_filename(filename):
     '''Returns a nice human readable path to 'filename'.'''
     a = os.path.abspath(filename)
     r = os.path.relpath(filename)
-    return a if len(a) < len(r) else r
+    return a if '..' in r else r