diff --git a/include/cow.h b/include/cow.h
index 7a3a6a4..f522720 100644
--- a/include/cow.h
+++ b/include/cow.h
@@ -18,6 +18,8 @@ enum cow_err_kind {
 	COW_ERR_SIZE,
 	/// `mmap()` failed.
 	COW_ERR_MAP,
+	/// Trying to use a poisoned cow
+	COW_ERR_POISONED,
 
 	_COW_ERR_SIZE,
 };
diff --git a/src/cow.c b/src/cow.c
index 6b9367f..2e8d355 100644
--- a/src/cow.c
+++ b/src/cow.c
@@ -122,7 +122,9 @@ void cow_free(cow_t* restrict cow)
 cow_t* cow_clone(const cow_t* cow)
 {
 	if(UNLIKELY(cow->poisoned)) {
+		_cow_set_err(COW_ERR_POISONED);
 		TRACE("WARNING: attempted to clone poisoned object at %p", (const void*)cow);
+	
 		return NULL;
 	}
 	cow_t clone;
diff --git a/src/error.cpp b/src/error.cpp
index ac3c41c..eb2da9e 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -21,6 +21,7 @@ namespace _cow_error {
 		setmsg(ret, COW_ERR_FDCREATE, "failed to create shmfd (memfd_create())");
 		setmsg(ret, COW_ERR_SIZE, "failed to set shmfd size (ftruncate())");
 		setmsg(ret, COW_ERR_MAP, "failed to map shmfd (mmap())");
+		setmsg(ret, COW_ERR_POISONED, "trying to use a poisoned cow");
 
 		return ret;
 	}