diff --git a/src/files.ml b/src/files.ml
index 25aabddef..3073b1f00 100644
--- a/src/files.ml
+++ b/src/files.ml
@@ -659,7 +659,7 @@ let diffCmd =
      ^ "Without any of these substrings, the two filenames will be appended to the command.  In all "
      ^ "cases, the filenames are suitably quoted.")
 
-let tempName s = Os.tempFilePrefix ^ s
+let tempName s = (Os.tempFilePrefix ()) ^ s
 
 let rec diff root1 path1 ui1 root2 path2 ui2 showDiff id =
   debug (fun () ->
diff --git a/src/os.ml b/src/os.ml
index ad27e217e..8a471e4e6 100644
--- a/src/os.ml
+++ b/src/os.ml
@@ -39,20 +39,33 @@ let serverHostName = localCanonicalHostName
 let myCanonicalHostName () =
   if !Trace.runningasserver then serverHostName else Prefs.read clientHostName
 
-let tempFilePrefix = ".unison."
-let tempFileSuffixFixed = ".unison.tmp"
-let tempFileSuffix = ref tempFileSuffixFixed
+let tempFilePrefixPref : string Prefs.t =
+  Prefs.createString "tempfileprefix" ".unison"
+    "!set the prefix for temporary files"
+    ("When specified, all filenames of temporary files created by unison" ^
+     "will begin with the set prefix.")
+
+let tempFileSuffixPref : string Prefs.t =
+  Prefs.createString "tempfilesuffix" ".unison.tmp"
+    "!set the suffix for temporary files"
+    ("When specified, all filenames of temporary files created by unison" ^
+     "will end with the set suffix.")
+
+let tempFilePrefix () = Prefs.read tempFilePrefixPref
+let tempFileSuffixFixed () = Prefs.read tempFileSuffixPref
+
+let tempFileSuffix = ref (tempFileSuffixFixed ())
 let includeInTempNames s =
   (* BCP: Added this in Jan 08.  If (as I believe) it never fails, then this tricky
      stuff can be deleted. *)
   assert (s<>"");
   tempFileSuffix :=
-    if s = "" then tempFileSuffixFixed
-    else "." ^ s ^ tempFileSuffixFixed
+    if s = "" then (tempFileSuffixFixed ())
+    else "." ^ s ^ (tempFileSuffixFixed ())
 
 let isTempFile file =
-  Util.endswith file tempFileSuffixFixed &&
-  Util.startswith file tempFilePrefix
+  Util.endswith file (tempFileSuffixFixed ()) &&
+  Util.startswith file (tempFilePrefix ())
 
 (*****************************************************************************)
 (*                      QUERYING THE FILESYSTEM                              *)
@@ -360,4 +373,5 @@ let genTempPath fresh fspath path prefix suffix =
   in f 0
 
 let tempPath ?(fresh=true) fspath path =
+  let tempFilePrefix = tempFilePrefix () in
   genTempPath fresh fspath path tempFilePrefix !tempFileSuffix
diff --git a/src/os.mli b/src/os.mli
index 8c08804f4..453de0489 100644
--- a/src/os.mli
+++ b/src/os.mli
@@ -4,7 +4,7 @@
 val myCanonicalHostName : unit -> string
 
 val tempPath : ?fresh:bool -> Fspath.t -> Path.local -> Path.local
-val tempFilePrefix : string
+val tempFilePrefix : unit -> string
 val isTempFile : string -> bool
 val includeInTempNames : string -> unit
 
diff --git a/src/uicommon.ml b/src/uicommon.ml
index 7eb1c42ca..fe391c8ca 100644
--- a/src/uicommon.ml
+++ b/src/uicommon.ml
@@ -545,7 +545,7 @@ let scanProfiles () =
            with Not_found -> ());
           (f, info))
        (Safelist.filter (fun name -> not (   Util.startswith name ".#"
-                                          || Util.startswith name Os.tempFilePrefix))
+                                          || Util.startswith name (Os.tempFilePrefix ())))
           (Files.ls Util.unisonDir "*.prf")))
 
 (* ---- *)