diff --git a/CHANGES.md b/CHANGES.md
index 114cdb747..7e28d2984 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -24,6 +24,9 @@
 - Fix a failure when using opam-monorepo with an opam 2.2 root
   (#379, @kit-ty-kate)
 
+- Fix assertion failure when prefix of "lock" subcommand is used (#381,
+  @gridbugs)
+
 ### Removed
 
 ### Security
diff --git a/cli/lock.ml b/cli/lock.ml
index 2b03938ce..b4e1f68e1 100644
--- a/cli/lock.ml
+++ b/cli/lock.ml
@@ -515,7 +515,7 @@ let extract_source_config ~adjustment ~opam_monorepo_cwd ~opam_files
 
 let raw_cli_args () =
   match Array.to_list Sys.argv with
-  | _bin :: "lock" :: args -> args
+  | _bin :: prefix :: args when String.starts_with ~prefix "lock" -> args
   | _ -> assert false
 
 let run (`Root root) (`Recurse_opam recurse) (`Build_only build_only)