diff --git a/tests/source/issue_5997.rs b/tests/source/issue_5997.rs
new file mode 100644
index 00000000000..d184c760f62
--- /dev/null
+++ b/tests/source/issue_5997.rs
@@ -0,0 +1,15 @@
+// rustfmt-version: Two
+
+// This formats with two spaces:
+pub struct Newtype(
+    /// Doc
+    #[doc()] //
+    pub  Vec<u8>,
+);
+
+// This formats with one:
+pub struct Newtype(
+    /// Doc
+    #[doc()]
+    pub Vec<u8>,
+);
diff --git a/tests/target/issue_5997.rs b/tests/target/issue_5997.rs
new file mode 100644
index 00000000000..881bc0fcb98
--- /dev/null
+++ b/tests/target/issue_5997.rs
@@ -0,0 +1,15 @@
+// rustfmt-version: Two
+
+// This formats with two spaces:
+pub struct Newtype(
+    /// Doc
+    #[doc()] //
+    pub Vec<u8>,
+);
+
+// This formats with one:
+pub struct Newtype(
+    /// Doc
+    #[doc()]
+    pub Vec<u8>,
+);