diff --git a/WDL/runtime/config_templates/default.cfg b/WDL/runtime/config_templates/default.cfg
index 0a9b23d0..dfef4676 100644
--- a/WDL/runtime/config_templates/default.cfg
+++ b/WDL/runtime/config_templates/default.cfg
@@ -93,11 +93,14 @@ output_hardlinks = false
 # output files would be deleted too. Input/output JSON, logs, and stdout/stderr are always retained
 # in the task run directory (above the container working directory).
 delete_work = false
-# In each task container, set TMPDIR environment variable to a subdirectory of the mounted task
-# working directory, automatically deleted afterwards. This may be useful if tasks use a lot of
-# scratch disk space and the run directory is on larger, separate storage from the container root
-# file system holding /tmp. Note the software inside the container must actually use the TMPDIR
-# environment variable in order for this to have an effect. (New in v1.5.4)
+# Suggest that each task's temporary directory should reside within the mounted task working
+# directory, instead of the storage backing the container's root filesystem. The latter (default)
+# is usually preferred because the working directory is more likely to reside on slower network-
+# attached storage. But mount_tmpdir may be helpful if tasks use large amounts of scratch space and
+# the working directory storage has more capacity.
+# The exact effect of this setting depends on the container backend implementation: some may change
+# where they mount /tmp, some may merely override TMPDIR inside the container, and others may not
+# yet implement it at all. (New in v1.5.4)
 mount_tmpdir = false
 # Selectively mount_tmpdir for those tasks whose names appear in this list. (New in v1.5.4)
 mount_tmpdir_for = []
diff --git a/WDL/runtime/task.py b/WDL/runtime/task.py
index 765c52b0..c157b594 100644
--- a/WDL/runtime/task.py
+++ b/WDL/runtime/task.py
@@ -494,7 +494,9 @@ def _eval_task_runtime(
     if cfg.get_bool("file_io", "mount_tmpdir") or task.name in cfg.get_list(
         "file_io", "mount_tmpdir_for"
     ):
-        env_vars_override["TMPDIR"] = os.path.join(container.container_dir, "work", "_tmpdir")
+        env_vars_override["TMPDIR"] = os.path.join(
+            container.container_dir, "work", "_miniwdl_tmpdir"
+        )
     if env_vars_override:
         # usually don't dump values into log, as they may often be auth tokens
         logger.notice(  # pyre-ignore
@@ -545,7 +547,7 @@ def _try_task(
         ):
             container.copy_input_files(logger)
         host_tmpdir = (
-            os.path.join(container.host_work_dir(), "_tmpdir")
+            os.path.join(container.host_work_dir(), "_miniwdl_tmpdir")
             if cfg.get_bool("file_io", "mount_tmpdir")
             or task.name in cfg.get_list("file_io", "mount_tmpdir_for")
             else None
@@ -554,13 +556,13 @@ def _try_task(
         try:
             # start container & run command
             if host_tmpdir:
-                logger.debug(_("creating temp directory to mount", TMPDIR=host_tmpdir))
+                logger.debug(_("creating task temp directory", TMPDIR=host_tmpdir))
                 os.mkdir(host_tmpdir, mode=0o770)
             try:
                 return container.run(logger, command)
             finally:
                 if host_tmpdir:
-                    logger.info(_("deleting mounted temp directory", TMPDIR=host_tmpdir))
+                    logger.info(_("deleting task temp directory", TMPDIR=host_tmpdir))
                     rmtree_atomic(host_tmpdir)
                 if (
                     "preemptible" in container.runtime_values