diff --git a/modules/services/unison.nix b/modules/services/unison.nix
index d7f8a628a..e32f70522 100644
--- a/modules/services/unison.nix
+++ b/modules/services/unison.nix
@@ -22,7 +22,7 @@ let
       };
 
       commandOptions = mkOption rec {
-        type = with types; attrsOf str;
+        type = with types; attrsOf (either str (listOf str));
         apply = mergeAttrs default;
         default = {
           repeat = "watch";
@@ -36,6 +36,8 @@ let
           Additional command line options as a dictionary to pass to the
           <literal>unison</literal> program.
           </para><para>
+          Use a list of strings to declare the same option multiple times.
+          </para><para>
           See
           <citerefentry>
             <refentrytitle>unison</refentrytitle>
@@ -60,7 +62,9 @@ let
     };
   };
 
-  serialiseArg = key: val: escapeShellArg "-${key}=${escape [ "=" ] val}";
+  serialiseArg = key: val:
+    concatStringsSep " "
+    (forEach (toList val) (x: escapeShellArg "-${key}=${escape [ "=" ] x}"));
 
   serialiseArgs = args: concatStringsSep " " (mapAttrsToList serialiseArg args);