diff --git a/src/doc/man/cargo-vendor.md b/src/doc/man/cargo-vendor.md
index f7c4532035c..917031bcc03 100644
--- a/src/doc/man/cargo-vendor.md
+++ b/src/doc/man/cargo-vendor.md
@@ -27,7 +27,7 @@ to use the vendored sources, which you will need to add to `.cargo/config.toml`.
 
 {{#option "`-s` _manifest_" "`--sync` _manifest_" }}
 Specify extra `Cargo.toml` manifests to workspaces which should also be
-vendored and synced to the output.
+vendored and synced to the output. Terminate the list with `--`.
 {{/option}}
 
 {{#option "`--no-delete`" }}
diff --git a/tests/testsuite/vendor.rs b/tests/testsuite/vendor.rs
index 947ff324fa8..6860708fa9f 100644
--- a/tests/testsuite/vendor.rs
+++ b/tests/testsuite/vendor.rs
@@ -309,6 +309,71 @@ fn two_lockfiles() {
     p.cargo("build").cwd("bar").run();
 }
 
+#[cargo_test]
+fn test_sync_argument() {
+    let p = project()
+        .no_manifest()
+        .file(
+            "foo/Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.1.0"
+
+                [dependencies]
+                bitflags = "=0.7.0"
+            "#,
+        )
+        .file("foo/src/lib.rs", "")
+        .file(
+            "bar/Cargo.toml",
+            r#"
+                [package]
+                name = "bar"
+                version = "0.1.0"
+
+                [dependencies]
+                bitflags = "=0.8.0"
+            "#,
+        )
+        .file("bar/src/lib.rs", "")
+        .file(
+            "baz/Cargo.toml",
+            r#"
+                [package]
+                name = "baz"
+                version = "0.1.0"
+
+                [dependencies]
+                bitflags = "=0.8.0"
+            "#,
+        )
+        .file("baz/src/lib.rs", "")
+        .build();
+
+    Package::new("bitflags", "0.7.0").publish();
+    Package::new("bitflags", "0.8.0").publish();
+
+    p.cargo("vendor --respect-source-config --manifest-path foo/Cargo.toml -s bar/Cargo.toml baz/Cargo.toml test_vendor")
+        .with_stderr("\
+error: failed to read [..]
+
+Caused by:
+  No such file or directory (os error 2)
+",
+        )
+        .with_status(101)
+        .run();
+
+    p.cargo("vendor --respect-source-config --manifest-path foo/Cargo.toml -s bar/Cargo.toml baz/Cargo.toml -- test_vendor")
+        .run();
+
+    let lock = p.read_file("test_vendor/bitflags/Cargo.toml");
+    assert!(lock.contains("version = \"0.8.0\""));
+    let lock = p.read_file("test_vendor/bitflags-0.7.0/Cargo.toml");
+    assert!(lock.contains("version = \"0.7.0\""));
+}
+
 #[cargo_test]
 fn delete_old_crates() {
     let p = project()