diff --git a/tools/afl/unmarshal_runner.janet b/tools/afl/unmarshal_runner.janet
index 801e8e00..31f43a53 100644
--- a/tools/afl/unmarshal_runner.janet
+++ b/tools/afl/unmarshal_runner.janet
@@ -1,2 +1,6 @@
- (pp (unmarshal (slurp ((dyn :args) 1)) load-image-dict))
-
+# Unmarshal garbage.
+(def v (unmarshal (slurp ((dyn :args) 1)) load-image-dict))
+# Trigger leaks or use after free.
+(gccollect)
+# Attempt to use generated value.
+(marshal v make-image-dict)