diff --git a/t/t4018/rust-macro-rules b/t/t4018/rust-macro-rules
new file mode 100644
index 0000000000..ec610c5b62
--- /dev/null
+++ b/t/t4018/rust-macro-rules
@@ -0,0 +1,6 @@
+macro_rules! RIGHT {
+    () => {
+        // a comment
+        let x = ChangeMe;
+    };
+}
diff --git a/userdiff.c b/userdiff.c
index 4e2b55a5e0..df85f0b8c5 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -165,7 +165,7 @@ PATTERNS("ruby", "^[ \t]*((class|module|def)[ \t].*)$",
 	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+|\\?(\\\\C-)?(\\\\M-)?."
 	 "|//=?|[-+*/<>%&^|=!]=|<<=?|>>=?|===|\\.{1,3}|::|[!=]~"),
 PATTERNS("rust",
-	 "^[\t ]*((pub(\\([^\\)]+\\))?[\t ]+)?((async|const|unsafe|extern([\t ]+\"[^\"]+\"))[\t ]+)?(struct|enum|union|mod|trait|fn|impl)[< \t]+[^;]*)$",
+	 "^[\t ]*((pub(\\([^\\)]+\\))?[\t ]+)?((async|const|unsafe|extern([\t ]+\"[^\"]+\"))[\t ]+)?(struct|enum|union|mod|trait|fn|impl|macro_rules!)[< \t]+[^;]*)$",
 	 /* -- */
 	 "[a-zA-Z_][a-zA-Z0-9_]*"
 	 "|[0-9][0-9_a-fA-Fiosuxz]*(\\.([0-9]*[eE][+-]?)?[0-9_fF]*)?"