diff --git a/base_dirs.go b/base_dirs.go
index fc482e2..0cdca02 100644
--- a/base_dirs.go
+++ b/base_dirs.go
@@ -1,6 +1,10 @@
 package xdg
 
-import "github.com/adrg/xdg/internal/pathutil"
+import (
+	"os"
+
+	"github.com/adrg/xdg/internal/pathutil"
+)
 
 // XDG Base Directory environment variables.
 const (
@@ -48,7 +52,13 @@ func (bd baseDirectories) cacheFile(relPath string) (string, error) {
 }
 
 func (bd baseDirectories) runtimeFile(relPath string) (string, error) {
-	return pathutil.Create(relPath, []string{bd.runtime})
+	var paths []string
+	for _, p := range pathutil.Unique([]string{bd.runtime, os.TempDir()}) {
+		if pathutil.Exists(p) {
+			paths = append(paths, p)
+		}
+	}
+	return pathutil.Create(relPath, paths)
 }
 
 func (bd baseDirectories) searchDataFile(relPath string) (string, error) {
diff --git a/xdg.go b/xdg.go
index 654d1d7..059d695 100644
--- a/xdg.go
+++ b/xdg.go
@@ -161,8 +161,9 @@ func CacheFile(relPath string) (string, error) {
 // The relPath parameter must contain the name of the runtime file, and
 // optionally, a set of parent directories (e.g. appname/app.pid).
 // If the specified directories do not exist, they will be created relative
-// to the base runtime directory. On failure, an error containing the
-// attempted paths is returned.
+// to the base runtime directory. If the base runtime directory does not exist,
+// the operating system's temporary directory is used as a fallback. On failure,
+// an error containing the attempted paths is returned.
 func RuntimeFile(relPath string) (string, error) {
 	return baseDirs.runtimeFile(relPath)
 }