diff --git a/sv-parser-pp/src/preprocess.rs b/sv-parser-pp/src/preprocess.rs
index 8564242..7ee2248 100644
--- a/sv-parser-pp/src/preprocess.rs
+++ b/sv-parser-pp/src/preprocess.rs
@@ -1191,7 +1191,7 @@ mod tests {
     #[test]
     fn ifndef_undefined() {
         let (ret, _) = preprocess(
-            testfile_path("test18.sv"),
+            testfile_path("ifndef_undefined.sv"),
             &HashMap::new(),
             &[] as &[String],
             false,
@@ -1200,7 +1200,7 @@ mod tests {
         .unwrap();
         assert_eq!(
             ret.text(),
-            testfile_contents("expected/ifndef_undefined")
+            testfile_contents("expected/ifndef_undefined.sv")
         );
     }
 
diff --git a/sv-parser-pp/testcases/expected/ifndef_undefined b/sv-parser-pp/testcases/expected/ifndef_undefined.sv
similarity index 100%
rename from sv-parser-pp/testcases/expected/ifndef_undefined
rename to sv-parser-pp/testcases/expected/ifndef_undefined.sv
diff --git a/sv-parser-pp/testcases/test18.sv b/sv-parser-pp/testcases/ifndef_undefined.sv
similarity index 100%
rename from sv-parser-pp/testcases/test18.sv
rename to sv-parser-pp/testcases/ifndef_undefined.sv