diff --git a/master_changes.md b/master_changes.md
index 8d07447fb8e..0b06f08639f 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -63,6 +63,7 @@ users)
   * Fix shell detection on Windows when opam is called via Cygwin's /usr/bin/env even though cmd/powershell is used [#5797 @kit-ty-kate]
   * Fix incorrect deduplication of environment variables on update. Effect was that FOO += "" would occlude the value of FOO in the environment [#5837 @dra27]
   * Fix regression from #5356 on the detection of out-of-date environment variables. As part of a refactoring, a filter predicate got inverted [#5837 @dra27]
+  * Unixify Windows paths in init shells scripts (sh, bash, zsh, fish & tsh) [#5797 @rjbou]
 
 ## Opamfile
 
@@ -101,6 +102,7 @@ users)
 ## Client
 
 ## Shell
+  * Quote all the paths to OPAMROOT when creating the init scripts on Unix in case OPAMROOT contains spaces, backslashes or special characters [#5841 @kit-ty-kate - fix #5804]
 
 ## Internal
 
diff --git a/src/core/opamSystem.mli b/src/core/opamSystem.mli
index 4023da622cf..de977c51c0d 100644
--- a/src/core/opamSystem.mli
+++ b/src/core/opamSystem.mli
@@ -202,8 +202,7 @@ val get_cygpath_function: command:string -> (string -> string) lazy_t
 val get_cygpath_path_transform: (pathlist:bool -> string -> string) lazy_t
 
 (** [apply_cygpath path] applies the `cygpath` command to [name] using
-    `cygpath -- name`. `cygpath` is resolved with default environment
-    in the function. *)
+    `cygpath -- name`. *)
 val apply_cygpath: string -> string
 
 (** [command cmd] executes the command [cmd] in the correct OPAM
diff --git a/src/state/opamEnv.ml b/src/state/opamEnv.ml
index 58f3dccb85c..42f4a30889e 100644
--- a/src/state/opamEnv.ml
+++ b/src/state/opamEnv.ml
@@ -875,16 +875,26 @@ let env_hook_script shell =
 
 let source root shell f =
   let fname = OpamFilename.to_string (OpamPath.init root // f) in
+  let unix_transform ?using_backslashes () =
+    let cygpath = Lazy.force OpamSystem.get_cygpath_path_transform in
+    cygpath ~pathlist:false fname
+    |> OpamStd.Env.escape_single_quotes ?using_backslashes
+  in
   match shell with
   | SH_csh ->
-    Printf.sprintf "if ( -f %s ) source %s >& /dev/null\n" fname fname
+    let fname = unix_transform () in
+    Printf.sprintf "if ( -f '%s' ) source '%s' >& /dev/null\n"
+      fname fname
   | SH_fish ->
-    Printf.sprintf "source %s > /dev/null 2> /dev/null; or true\n" fname
+    let fname = unix_transform ~using_backslashes:true () in
+    Printf.sprintf "source '%s' > /dev/null 2> /dev/null; or true\n" fname
   | SH_sh | SH_bash ->
-    Printf.sprintf "test -r %s && . %s > /dev/null 2> /dev/null || true\n"
+    let fname = unix_transform () in
+    Printf.sprintf "test -r '%s' && . '%s' > /dev/null 2> /dev/null || true\n"
       fname fname
   | SH_zsh ->
-    Printf.sprintf "[[ ! -r %s ]] || source %s  > /dev/null 2> /dev/null\n"
+    let fname = unix_transform () in
+    Printf.sprintf "[[ ! -r '%s' ]] || source '%s' > /dev/null 2> /dev/null\n"
       fname fname
   | SH_cmd ->
     Printf.sprintf "if exist \"%s\" call \"%s\" >NUL 2>NUL\n" fname fname