diff --git a/lib/vfs/src/lib.rs b/lib/vfs/src/lib.rs
index 580905e5983..c41c285aca4 100644
--- a/lib/vfs/src/lib.rs
+++ b/lib/vfs/src/lib.rs
@@ -2,6 +2,7 @@ use std::any::Any;
 use std::ffi::OsString;
 use std::fmt;
 use std::io;
+use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::pin::Pin;
 use std::task::Context;
@@ -71,6 +72,27 @@ pub trait FileSystem: fmt::Debug + Send + Sync + 'static + Upcastable {
     fn remove_file(&self, path: &Path) -> Result<()>;
 
     fn new_open_options(&self) -> OpenOptions;
+
+    /// Create a directory and all its parent directories.
+    fn create_dir_all(&self, path: &Path) -> Result<()> {
+        create_dir_all(self, path)
+    }
+}
+
+fn create_dir_all(fs: &(impl FileSystem + ?Sized), path: &Path) -> Result<()> {
+    match fs.create_dir(path) {
+        Ok(_) | Err(FsError::AlreadyExists) => Ok(()),
+        Err(FsError::EntryNotFound) => {
+            // Note: paths don't normally have many segments, so it should be
+            // fine to use recursion here. This function should also be elegible
+            // for TCO.
+            match path.parent() {
+                Some(parent) => create_dir_all(fs, parent),
+                None => Err(FsError::EntryNotFound),
+            }
+        }
+        Err(e) => Err(e),
+    }
 }
 
 impl dyn FileSystem + 'static {
@@ -84,6 +106,40 @@ impl dyn FileSystem + 'static {
     }
 }
 
+impl<D, F> FileSystem for D
+where
+    D: Deref<Target = F> + std::fmt::Debug + Send + Sync + 'static,
+    F: FileSystem + ?Sized,
+{
+    fn read_dir(&self, path: &Path) -> Result<ReadDir> {
+        (**self).read_dir(path)
+    }
+
+    fn create_dir(&self, path: &Path) -> Result<()> {
+        (**self).create_dir(path)
+    }
+
+    fn remove_dir(&self, path: &Path) -> Result<()> {
+        (**self).remove_dir(path)
+    }
+
+    fn rename(&self, from: &Path, to: &Path) -> Result<()> {
+        (**self).rename(from, to)
+    }
+
+    fn metadata(&self, path: &Path) -> Result<Metadata> {
+        (**self).metadata(path)
+    }
+
+    fn remove_file(&self, path: &Path) -> Result<()> {
+        (**self).remove_file(path)
+    }
+
+    fn new_open_options(&self) -> OpenOptions {
+        (**self).new_open_options()
+    }
+}
+
 pub trait FileOpener {
     fn open(
         &self,
diff --git a/lib/wasi/src/runners/container.rs b/lib/wasi/src/runners/container.rs
index 955e77ea070..a41830b7ddf 100644
--- a/lib/wasi/src/runners/container.rs
+++ b/lib/wasi/src/runners/container.rs
@@ -111,10 +111,10 @@ impl WapmContainer {
 
     /// Get the entire container as a single filesystem and a list of suggested
     /// directories to preopen.
-    pub(crate) fn container_fs(&self) -> Arc<dyn FileSystem + Send + Sync> {
+    pub(crate) fn container_fs(&self) -> Box<dyn FileSystem + Send + Sync> {
         match &self.repr {
-            Repr::V1Mmap(mapped) => Arc::new(WebcFileSystem::init_all(Arc::clone(mapped))),
-            Repr::V1Owned(owned) => Arc::new(WebcFileSystem::init_all(Arc::clone(owned))),
+            Repr::V1Mmap(mapped) => Box::new(WebcFileSystem::init_all(Arc::clone(mapped))),
+            Repr::V1Owned(owned) => Box::new(WebcFileSystem::init_all(Arc::clone(owned))),
         }
     }
 }
diff --git a/lib/wasi/src/runners/wasi.rs b/lib/wasi/src/runners/wasi.rs
index f00bd28ec89..902ebd555c4 100644
--- a/lib/wasi/src/runners/wasi.rs
+++ b/lib/wasi/src/runners/wasi.rs
@@ -194,13 +194,25 @@ fn unioned_filesystem(
     mapped_dirs: &[MappedDirectory],
     container: &WapmContainer,
 ) -> Result<impl FileSystem, Error> {
-    let root_fs = RootFileSystemBuilder::new().build();
+    let mut fs = wasmer_vfs::UnionFileSystem::new();
 
-    let filesystem = container.container_fs();
-    root_fs.union(&filesystem);
+    // First, mount the root filesystem so we get things like "/dev/"
+    fs.mount(
+        "base",
+        "/",
+        false,
+        Box::new(RootFileSystemBuilder::new().build()),
+        None,
+    );
 
+    // We also want the container's volumes
+    fs.mount("webc", "/", false, container.container_fs(), None);
+
+    // Now, let's merge in the host volumes.
     if !mapped_dirs.is_empty() {
-        let fs_backing: Arc<dyn FileSystem + Send + Sync> =
+        let mapped_fs = wasmer_vfs::TmpFileSystem::new();
+
+        let host_fs: Arc<dyn FileSystem + Send + Sync> =
             Arc::new(PassthruFileSystem::new(crate::default_fs_backing()));
 
         for MappedDirectory { host, guest } in mapped_dirs.iter() {
@@ -214,8 +226,12 @@ fn unioned_filesystem(
                 "mounting host directory",
             );
 
-            root_fs
-                .mount(guest.clone(), &fs_backing, host.clone())
+            if let Some(parent) = guest.parent() {
+                mapped_fs.create_dir_all(parent.as_ref())?;
+            }
+
+            mapped_fs
+                .mount(guest.clone(), &host_fs, host.clone())
                 .with_context(|| {
                     format!(
                         "Unable to mount \"{}\" to \"{}\"",
@@ -224,9 +240,11 @@ fn unioned_filesystem(
                     )
                 })?;
         }
+
+        fs.mount("host", "/", true, Box::new(mapped_fs), None);
     }
 
-    Ok(root_fs)
+    Ok(fs)
 }
 
 #[cfg(test)]