diff --git a/asn1c/tests/data-126/README b/asn1c/tests/data-126/README
index 19fa8684..07ff013e 100644
--- a/asn1c/tests/data-126/README
+++ b/asn1c/tests/data-126/README
@@ -4,3 +4,7 @@ Mode of operation:
 	then compared with the .out file, then decoded back into XER
 	and compared to the original .in file content.
 
+Naming conventions:
+
+*-P.in  -       PER decoding of .out file must fail.
+
diff --git a/asn1c/tests/data-126/data-126-02.in b/asn1c/tests/data-126/data-126-02-P.in
similarity index 100%
rename from asn1c/tests/data-126/data-126-02.in
rename to asn1c/tests/data-126/data-126-02-P.in
diff --git a/asn1c/tests/data-126/data-126-02.out b/asn1c/tests/data-126/data-126-02-P.out
similarity index 100%
rename from asn1c/tests/data-126/data-126-02.out
rename to asn1c/tests/data-126/data-126-02-P.out