diff --git a/testdata/parser/negative/20.txt b/testdata/parser/negative/20.txt
new file mode 100644
index 0000000000000000000000000000000000000000..41f6d4d1d7e99f9f2719619dab57624c85068f43
--- /dev/null
+++ b/testdata/parser/negative/20.txt
@@ -0,0 +1,3 @@
+Parse error at 20.pdl:6:10: Unindexable expression
+	x[1] = x[1][0:1];
+	        ^