diff --git a/lib/session.ml b/lib/session.ml
index ddfb794..540bd39 100644
--- a/lib/session.ml
+++ b/lib/session.ml
@@ -80,15 +80,21 @@ let package_of t origin =
   match origin with
   | "" -> None
   | origin ->
-    let dir =
-      try Filename.dirname (Unix.realpath origin)
-      with Unix.Unix_error _ -> Filename.dirname origin
+    let here =
+      try Unix.realpath origin with Unix.Unix_error _ -> origin
     in
+    let dir = Filename.dirname here in
+    (* A package is a directory, or a single .flan file named outright — so the
+       file being edited belongs to it if the package *is* that file, or if it
+       sits in the package's directory. Comparing only the directory would miss
+       the file case entirely and answer [None], which is the silent failure
+       above rather than a loud one: the form splices unqualified and the
+       running program keeps calling the name it already had. *)
     let same p =
       let d =
         try Unix.realpath p.Load.dir with Unix.Unix_error _ -> p.Load.dir
       in
-      String.equal d dir
+      String.equal d here || String.equal d dir
     in
     (match List.filter same t.pkgs with
      | [] -> None
diff --git a/test/test_session.ml b/test/test_session.ml
index 70469a8..5a6ba7f 100644
--- a/test/test_session.ml
+++ b/test/test_session.ml
@@ -167,6 +167,19 @@ let () =
        fail "a form from a package file reported %s, wanted agent/poll"
          (String.concat " " c.Session.fns)
    | exception Loc.Error (_, m) -> fail "redefining agent/poll: %s" m);
+  (* A package that is a single file, which is what sand.flan is to the
+     headless driver. The file being edited *is* the package rather than a
+     member of a directory, so matching on the directory alone would answer
+     "not a package" — and the failure is the silent one above: the form
+     splices as a bare [step] and the running program keeps the one it had. *)
+  let t2, _ = Session.create ~file:"programs/sand-headless.flan" in
+  (match Session.eval ~origin:"../sand.flan" t2 "(defn step [] Unit (do))" with
+   | c ->
+     if c.Session.fns <> [ "sand/step" ] then
+       fail "a form from a single-file package reported %s, wanted sand/step"
+         (String.concat " " c.Session.fns)
+   | exception Loc.Error (_, m) -> fail "redefining sand/step: %s" m);
+
   (* And a file that is not a package keeps its names as written. *)
   (match Session.eval ~origin:"../sand.flan" t "(defn game-draw [] Unit (do))" with
    | c ->