diff --git a/lib/pure/os.nim b/lib/pure/os.nim
index 6cf5e1fb7e..84f492c9df 100644
--- a/lib/pure/os.nim
+++ b/lib/pure/os.nim
@@ -296,6 +296,26 @@ proc setCurrentDir*(newDir: string) {.inline, tags: [].} =
   else:
     if chdir(newDir) != 0'i32: raiseOSError(osLastError())
 
+proc absolutePath*(path: string, root = getCurrentDir()): string =
+  ## Returns the absolute path of `path`, rooted at `root` (which must be absolute)
+  ## if `path` is absolute, return it, ignoring `root`
+  runnableExamples:
+    doAssert absolutePath("a") == getCurrentDir() / "a"
+  if isAbsolute(path): path
+  else:
+    if not root.isAbsolute:
+      raise newException(ValueError, "The specified root is not absolute: " & root)
+    joinPath(root, path)
+
+when isMainModule:
+  doAssertRaises(ValueError): discard absolutePath("a", "b")
+  doAssert absolutePath("a") == getCurrentDir() / "a"
+  doAssert absolutePath("a", "/b") == "/b" / "a"
+  when defined(Posix):
+    doAssert absolutePath("a", "/b/") == "/b" / "a"
+    doAssert absolutePath("a", "/b/c") == "/b/c" / "a"
+    doAssert absolutePath("/a", "b/") == "/a"
+
 proc expandFilename*(filename: string): string {.rtl, extern: "nos$1",
   tags: [ReadDirEffect].} =
   ## Returns the full (`absolute`:idx:) path of an existing file `filename`,