diff --git a/internal/datafs/fsurl.go b/internal/datafs/fsurl.go
index a1cf5cbca..f34324a0c 100644
--- a/internal/datafs/fsurl.go
+++ b/internal/datafs/fsurl.go
@@ -21,6 +21,15 @@ func SplitFSMuxURL(in *url.URL) (*url.URL, string) {
 		}
 
 		return &u, base
+	case "aws+sm":
+		// An aws+sm URL can either be opaque or have a path with a leading
+		// slash. If it's opaque, the URL must not contain a leading slash. If
+		// it has a path, the URL must begin with a slash.
+		if u.Opaque != "" {
+			return &url.URL{Scheme: u.Scheme}, u.Opaque
+		} else {
+			return &url.URL{Scheme: u.Scheme, Path: "/"}, strings.TrimLeft(u.Path, "/")
+		}
 	}
 
 	// trim leading and trailing slashes - they are not part of a valid path
diff --git a/internal/datafs/fsurl_test.go b/internal/datafs/fsurl_test.go
index 00bba69b0..bcfa3c862 100644
--- a/internal/datafs/fsurl_test.go
+++ b/internal/datafs/fsurl_test.go
@@ -95,6 +95,26 @@ func TestSplitFSMuxURL(t *testing.T) {
 			"merge:///",
 			"vault:///foo/bar|foo|git+ssh://git@github.com/hairyhenderson/go-which.git//a/b/c/d",
 		},
+		{
+			"aws+sm:foo",
+			"aws+sm:",
+			"foo",
+		},
+		{
+			"aws+sm:foo/bar",
+			"aws+sm:",
+			"foo/bar",
+		},
+		{
+			"aws+sm:/foo/bar",
+			"aws+sm:///",
+			"foo/bar",
+		},
+		{
+			"aws+sm:/foo",
+			"aws+sm:///",
+			"foo",
+		},
 	}
 
 	for _, d := range testdata {
diff --git a/internal/datafs/fsys.go b/internal/datafs/fsys.go
index 03abdf6d6..1102fb8a2 100644
--- a/internal/datafs/fsys.go
+++ b/internal/datafs/fsys.go
@@ -55,6 +55,8 @@ func FSysForPath(ctx context.Context, path string) (fs.FS, error) {
 	switch u.Scheme {
 	case "git+http", "git+https", "git+ssh", "git":
 		// no-op, these are handled
+	case "aws+sm":
+		// An aws+sm URL can be opaque, best not disturb it
 	case "", "file", "git+file":
 		// default to "/" so we have a rooted filesystem for all schemes, but also
 		// support volumes on Windows
diff --git a/internal/datafs/reader.go b/internal/datafs/reader.go
index 68d5d37f7..52ebefe1c 100644
--- a/internal/datafs/reader.go
+++ b/internal/datafs/reader.go
@@ -122,13 +122,13 @@ func (d *dsReader) readFileContent(ctx context.Context, u *url.URL, hdr http.Hea
 	// leaking into the filesystem layer
 	u = removeQueryParam(u, overrideType)
 
+	u, fname := SplitFSMuxURL(u)
+
 	fsys, err := FSysForPath(ctx, u.String())
 	if err != nil {
 		return nil, fmt.Errorf("fsys for path %v: %w", u, err)
 	}
 
-	u, fname := SplitFSMuxURL(u)
-
 	// need to support absolute paths on local filesystem too
 	// TODO: this is a hack, probably fix this?
 	if u.Scheme == "file" && runtime.GOOS != "windows" {