diff --git a/act/container/docker_run.go b/act/container/docker_run.go
index 5b3f7814..04ea67dd 100644
--- a/act/container/docker_run.go
+++ b/act/container/docker_run.go
@@ -1158,9 +1158,9 @@ func parseOptionsHostConfig(options string) (*container.HostConfig, error) {
 // sanitizeConfig remove the invalid configurations from `config` and `hostConfig`
 func (cr *containerReference) sanitizeConfig(ctx context.Context, config *container.Config, hostConfig *container.HostConfig) (*container.Config, *container.HostConfig) {
 	logger := common.Logger(ctx)
+	matcher := newValidVolumeMatcher(ctx, cr.input.ValidVolumes)
 
 	if len(cr.input.ValidVolumes) > 0 {
-		matcher := newValidVolumeMatcher(ctx, cr.input.ValidVolumes)
 		// sanitize binds
 		sanitizedBinds := make([]string, 0, len(hostConfig.Binds))
 		for _, bind := range hostConfig.Binds {
@@ -1181,26 +1181,22 @@ func (cr *containerReference) sanitizeConfig(ctx context.Context, config *contai
 			}
 		}
 		hostConfig.Binds = sanitizedBinds
-		// sanitize mounts
-		sanitizedMounts := make([]mount.Mount, 0, len(hostConfig.Mounts))
-		for _, mt := range hostConfig.Mounts {
-			if matcher.isValid(mt.Source, mt.Type) {
-				sanitizedMounts = append(sanitizedMounts, mt)
-			} else {
-				logger.Warnf("[%s] is not a valid volume, will be ignored", mt.Source)
-			}
-		}
-		hostConfig.Mounts = sanitizedMounts
 	} else {
 		for _, bind := range hostConfig.Binds {
 			logger.Warnf("[%s] is not a valid volume, will be ignored", bind)
 		}
-		for _, mt := range hostConfig.Mounts {
+		hostConfig.Binds = []string{}
+	}
+	// sanitize mounts
+	sanitizedMounts := make([]mount.Mount, 0, len(hostConfig.Mounts))
+	for _, mt := range hostConfig.Mounts {
+		if matcher.isValid(mt.Source, mt.Type) {
+			sanitizedMounts = append(sanitizedMounts, mt)
+		} else {
 			logger.Warnf("[%s] is not a valid volume, will be ignored", mt.Source)
 		}
-		hostConfig.Binds = []string{}
-		hostConfig.Mounts = []mount.Mount{}
 	}
+	hostConfig.Mounts = sanitizedMounts
 
 	return config, hostConfig
 }
@@ -1284,6 +1280,9 @@ func (m validVolumeMatcher) isValid(source string, sourceType mount.Type) bool {
 	if m.allowAll {
 		return true
 	}
+	if sourceType == mount.TypeTmpfs && source == "" { // backed by memory, exposes nothing from the host, same as --tmpfs
+		return true
+	}
 	if isHostVolumeSource(source, sourceType) {
 		normalized, err := normalizeHostVolumePath(source)
 		if err != nil {
diff --git a/act/container/docker_run_test.go b/act/container/docker_run_test.go
index c7aeb751..70c40ed0 100644
--- a/act/container/docker_run_test.go
+++ b/act/container/docker_run_test.go
@@ -762,6 +762,22 @@ func TestCheckVolumesRejectsEscapingHostPaths(t *testing.T) {
 	assert.Empty(t, hostConf.Binds)
 }
 
+func TestSanitizeConfigKeepsTmpfsMounts(t *testing.T) {
+	hostConfig, _ := mergeOptions(t, "", "--mount type=tmpfs,dst=/var/lib/mysql", false)
+	require.Len(t, hostConfig.Mounts, 1)
+
+	for _, validVolumes := range [][]string{nil, {"data"}} {
+		logger, hook := test.NewNullLogger()
+		_, sanitized := (&containerReference{input: &NewContainerInput{ValidVolumes: validVolumes}}).sanitizeConfig(common.WithLogger(context.Background(), logger), &container.Config{}, &container.HostConfig{Mounts: []mount.Mount{
+			hostConfig.Mounts[0],
+			{Type: mount.TypeVolume, Target: "/anonymous"},
+			{Type: mount.TypeTmpfs, Source: "/etc", Target: "/etc-copy"},
+		}})
+		assert.Equal(t, hostConfig.Mounts, sanitized.Mounts)
+		assert.Len(t, hook.AllEntries(), 2)
+	}
+}
+
 func TestContainerInfoFromInspect(t *testing.T) {
 	t.Run("reports no healthcheck when the image declares none", func(t *testing.T) {
 		info := containerInfoFromInspect(container.InspectResponse{
diff --git a/internal/pkg/config/config.example.yaml b/internal/pkg/config/config.example.yaml
index 89f8b78a..fb33dc2c 100644
--- a/internal/pkg/config/config.example.yaml
+++ b/internal/pkg/config/config.example.yaml
@@ -237,14 +237,13 @@ container:
   # If it's empty, /workspace will be used.
   # Purely numeric subdirectories under this path are reserved for task workspaces and may be removed by idle cleanup.
   #workdir_parent:
-  # Volumes (including bind mounts) can be mounted to containers. Glob syntax is supported, see https://github.com/bmatcuk/doublestar#patterns
-  # `*` matches within a single path segment, `**` also matches across path separators.
-  # You can specify multiple volumes. If the sequence is empty, no volumes can be mounted.
-  # For example, if you only allow containers to mount the `data` volume and all the json files in `/src`, you should change the config to:
+  # Volumes and bind mounts containers may mount, as globs (https://github.com/bmatcuk/doublestar#patterns).
+  # `*` matches within a path segment, `**` across segments. Empty allows none. tmpfs mounts are always allowed.
+  # For example, to allow the `data` volume and all json files in `/src`:
   # valid_volumes:
   #   - data
   #   - /src/*.json
-  # If you want to allow any volume, please use the following configuration:
+  # To allow any volume:
   # valid_volumes:
   #   - '**'
   #valid_volumes: []