diff --git a/validphys2/src/validphys/checks.py b/validphys2/src/validphys/checks.py
index 00ee0bcf7d..6094dcc94d 100644
--- a/validphys2/src/validphys/checks.py
+++ b/validphys2/src/validphys/checks.py
@@ -54,7 +54,7 @@ def check_pdf_is_montecarlo_or_hessian(pdf, **kwargs):
 
 @make_argcheck
 def check_not_using_pdferr(use_pdferr, **kwargs):
-    check(not use_pdferr, "The flag 'use_pdferr' must be off to use this function")
+    check(not use_pdferr, "The flag 'use_pdferr' must be `False` to use this function. This is to avoid including the PDF error in the uncertainty bars of the experimental datapoints.")
 
 
 @make_check