diff --git a/test/Misc/diag-mapping.c b/test/Misc/diag-mapping.c
index 73a36ee..dc07e0d 100644
--- a/test/Misc/diag-mapping.c
+++ b/test/Misc/diag-mapping.c
@@ -9,6 +9,9 @@
 // -Werror can map this one warning to error.
 // RUN: clang-cc %s -Werror=extra-tokens 2>&1 | grep "error:" &&
 
+// Mapping unrelated diags to errors doesn't affect this one.
+// RUN: clang-cc %s -Werror=trigraphs 2>&1 | grep "warning:" &&
+
 // This should stay a warning with -pedantic.
 // RUN: clang-cc %s -pedantic 2>&1 | grep "warning:" &&