diff --git a/Changes b/Changes
index b3b44655f..ffe152fe2 100644
--- a/Changes
+++ b/Changes
@@ -206,6 +206,7 @@ Bug fixes:
 - PR#6812: -short-paths and -no-alias-deps can create inconsistent assumptions
 - PR#6817: GADT exhaustiveness breakage with modules
 - PR#6836: Assertion failure using -short-paths
+- PR#6841: Changing compilation unit name with -o breaks ocamldebug
 - GPR#143: fix getsockopt behaviour for boolean socket options
   (Anil Madhavapeddy and Andrew Ray)
 - ocamlbuild on cygwin cannot find ocamlfind
diff --git a/debugger/command_line.ml b/debugger/command_line.ml
index 2c551c3d5..9fa9ff9d8 100644
--- a/debugger/command_line.ml
+++ b/debugger/command_line.ml
@@ -639,8 +639,12 @@ let instr_break ppf lexbuf =
         let module_name = convert_module (module_of_longident mdle) in
         new_breakpoint
           (try
+            let ev =  event_at_pos module_name 0 in
+            let ev_pos =
+              {Lexing.dummy_pos with
+               pos_fname = (Events.get_pos ev).pos_fname} in
              let buffer =
-               try get_buffer Lexing.dummy_pos module_name with
+               try get_buffer ev_pos module_name with
                | Not_found ->
                   eprintf "No source file for %s.@." module_name;
                   raise Toplevel
diff --git a/debugger/source.ml b/debugger/source.ml
index aa9ec7083..fa2b3c7e4 100644
--- a/debugger/source.ml
+++ b/debugger/source.ml
@@ -21,6 +21,8 @@ let source_extensions = [".ml"]
 (*** Conversion function. ***)
 
 let source_of_module pos mdle =
+  let pos_fname = pos.Lexing.pos_fname in
+  if Sys.file_exists pos_fname then pos_fname else
   let is_submodule m m' =
     let len' = String.length m' in
     try