diff --git a/src_teal/texrunner/pathutil_unix.tl b/src_teal/texrunner/pathutil_unix.tl
index 291aa17..9913239 100644
--- a/src_teal/texrunner/pathutil_unix.tl
+++ b/src_teal/texrunner/pathutil_unix.tl
@@ -168,18 +168,20 @@ local function joinpath2(x: string, y: string): string
   end
 end
 
-local function joinpath(...: string): string
-  local args = {...}
+local function joinpath(a?:string, b?:string, ...: string): string
   local n = select("#", ...)
-  if n == 2 then
-    return joinpath2(args[1], args[2])
-  elseif n == 0 then
+  if not a then
+    -- 0 argument
     return "."
-  elseif n == 1 then
-    return ...
+  elseif not b then
+    -- 1 argument
+    return a
+  elseif n == 0 then
+    -- 2 arguments
+    return joinpath2(a, b)
   else
-    -- n is >= 3
-    return joinpath(joinpath2(args[1], args[2]), select(3, ...))
+    -- >= 3 arguments
+    return joinpath(joinpath2(a, b), ...)
   end
 end
 
diff --git a/src_teal/texrunner/pathutil_windows.tl b/src_teal/texrunner/pathutil_windows.tl
index 0c7396f..ccb0508 100644
--- a/src_teal/texrunner/pathutil_windows.tl
+++ b/src_teal/texrunner/pathutil_windows.tl
@@ -174,18 +174,20 @@ local function joinpath2(x: string, y: string): string
   end
 end
 
-local function joinpath(...: string): string
-  local args = {...}
+local function joinpath(a?:string, b?:string, ...: string): string
   local n = select("#", ...)
-  if n == 2 then
-    return joinpath2(args[1], args[2])
-  elseif n == 0 then
+  if not a then
+    -- 0 argument
     return "."
-  elseif n == 1 then
-    return ...
+  elseif not b then
+    -- 1 argument
+    return a
+  elseif n == 0 then
+    -- 2 arguments
+    return joinpath2(a, b)
   else
-    -- n is >= 3
-    return joinpath(joinpath2(args[1], args[2]), select(3, ...))
+    -- >= 3 arguments
+    return joinpath(joinpath2(a, b), ...)
   end
 end