diff --git a/analysis/test_cases/neg_duplicate_decl.mg b/analysis/test_cases/neg_duplicate_decl.mg
new file mode 100644
index 0000000..0fabaed
--- /dev/null
+++ b/analysis/test_cases/neg_duplicate_decl.mg
@@ -0,0 +1,8 @@
+# Test case for issue #25 - duplicate declarations should cause an error
+
+Decl foo(X, Y, Z) descr [ extensional() ] bound [/x, /y, /z].
+
+# This should cause an error - duplicate declaration
+Decl foo(X, Y, Z) descr [ extensional() ].
+
+foo(1, 2, 3).
\ No newline at end of file