diff --git a/src/formatting/lists.rs b/src/formatting/lists.rs
index 1dcd7044d5d..2678adf1c44 100644
--- a/src/formatting/lists.rs
+++ b/src/formatting/lists.rs
@@ -417,7 +417,12 @@ where
             result.push_str(&formatted_comment);
         }
 
-        if separate && sep_place.is_back() {
+        let need_extra_separator = separate
+            && last
+            && item.post_comment.as_ref().map_or(true, |cmnt| {
+                cmnt.find_uncommented(formatting.separator).is_none()
+            });
+        if separate && sep_place.is_back() && (!last || need_extra_separator) {
             result.push_str(formatting.separator);
         }
 
@@ -733,6 +738,7 @@ pub(crate) fn extract_post_comment(
 
     // Cleanup post-comment: strip separators and whitespace.
     let post_snippet = post_snippet[..comment_end].trim();
+    let mut _post_snippet_without_sep = String::new();
     let post_snippet_trimmed = if post_snippet.starts_with(|c| c == ',' || c == ':') {
         post_snippet[1..].trim_matches(white_space)
     } else if let Some(post_snippet) = post_snippet.strip_prefix(separator) {
@@ -743,6 +749,19 @@ pub(crate) fn extract_post_comment(
         && (!post_snippet.trim().starts_with("//") || post_snippet.trim().contains('\n'))
     {
         post_snippet[..(post_snippet.len() - 1)].trim_matches(white_space)
+    } else if let Some(sep_pos) = post_snippet.find_uncommented(",") {
+        _post_snippet_without_sep = [
+            post_snippet[..sep_pos]
+                .trim_matches(white_space)
+                .trim_matches('\n'),
+            "\n",
+            post_snippet[sep_pos + separator.len()..]
+                .trim_matches(white_space)
+                .trim_matches('\n'),
+        ]
+        .concat();
+
+        &_post_snippet_without_sep
     } else {
         post_snippet
     };
diff --git a/tests/source/issue-3876.rs b/tests/source/issue-3876.rs
new file mode 100644
index 00000000000..426fbf287bf
--- /dev/null
+++ b/tests/source/issue-3876.rs
@@ -0,0 +1,58 @@
+fn f<S>(s: S)
+where
+    S: Send /* */,
+      //
+{
+}
+
+fn main() {
+    foo(
+        x 
+	// comment 1
+        ,
+        // comment 2
+    )
+}
+
+fn main() {
+    foo(
+        x
+        // comment 1
+
+
+        ,
+
+
+
+        // comment 2
+    )
+}
+
+fn main() {
+    foo(
+        x 
+	/* Comment 1 */
+        ,
+        /* Comment 2 */
+    )
+}
+
+fn main() {
+    foo(
+        x    /* Comment 1 */     ,   /* Comment 2 */
+    )
+}
+
+fn main() {
+    foo(
+        x
+        /* comment 1 */
+
+
+        ,
+
+
+
+        /* comment 2 */
+    )
+}
diff --git a/tests/source/issue-4714.rs b/tests/source/issue-4714.rs
new file mode 100644
index 00000000000..881e214cc59
--- /dev/null
+++ b/tests/source/issue-4714.rs
@@ -0,0 +1,3 @@
+struct Something {
+    field: u32/*a*/,/*b*/
+}
diff --git a/tests/target/issue-3876.rs b/tests/target/issue-3876.rs
new file mode 100644
index 00000000000..fb0078c3ccb
--- /dev/null
+++ b/tests/target/issue-3876.rs
@@ -0,0 +1,41 @@
+fn f<S>(s: S)
+where
+    S: Send, /* */
+    //
+{
+}
+
+fn main() {
+    foo(
+        x, // comment 1
+        // comment 2
+    )
+}
+
+fn main() {
+    foo(
+        x, // comment 1
+        // comment 2
+    )
+}
+
+fn main() {
+    foo(
+        x, /* Comment 1 */
+        /* Comment 2 */
+    )
+}
+
+fn main() {
+    foo(
+        x, /* Comment 1 */
+        /* Comment 2 */
+    )
+}
+
+fn main() {
+    foo(
+        x, /* comment 1 */
+        /* comment 2 */
+    )
+}
diff --git a/tests/target/issue-4714.rs b/tests/target/issue-4714.rs
new file mode 100644
index 00000000000..ca4f2159cc6
--- /dev/null
+++ b/tests/target/issue-4714.rs
@@ -0,0 +1,4 @@
+struct Something {
+    field: u32, /*a*/
+    /*b*/
+}