diff --git a/SC2109.md b/SC2109.md
new file mode 100644
index 0000000..3c24e56
--- /dev/null
+++ b/SC2109.md
@@ -0,0 +1,17 @@
+## Instead of [ a || b ], use [ a ] || [ b ].
+
+### Problematic code:
+
+    [ "$1" = "-v" || "$1" = "-help" ]
+
+### Correct code:
+
+    [ "$1" = "-v" ] || [ "$1" = "-help" ]
+
+### Rationale:
+
+`||` can not be used in a `[ .. ]` test expression. Instead, make two `[ .. ]` expressions and put the `||` between them.
+
+### Exceptions:
+
+None.
\ No newline at end of file