diff --git a/CHANGES.md b/CHANGES.md
index 8dc3f5588..8059e5c2d 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,8 +1,12 @@
 # Unreleased
 
+## Fixes
+
 - Fix debouncing of document updates. It was essentially complicated broken in
   all but the most trivial cases. (#509 fixes #504)
 
+- Fix completion when passing named and functional arguments (#512)
+
 # 1.8.2 (09/14/2021)
 
 - Disable experimental dune support. It was accidentally left enabled.
diff --git a/ocaml-lsp-server/src/compl.ml b/ocaml-lsp-server/src/compl.ml
index e106803e4..20f1cc150 100644
--- a/ocaml-lsp-server/src/compl.ml
+++ b/ocaml-lsp-server/src/compl.ml
@@ -27,6 +27,7 @@ let completion_kind kind : CompletionItemKind.t option =
   | `MethodCall -> Some Method
   | `Keyword -> Some Keyword
 
+(** @see https://ocaml.org/manual/lex.html reference *)
 let prefix_of_position ~short_path source position =
   match Msource.text source with
   | "" -> ""
@@ -87,7 +88,18 @@ let prefix_of_position ~short_path source position =
       | Some pos -> pos + 1
     in
     let len = from - pos + 1 in
-    String.sub text ~pos ~len
+    let reconstructed_prefix = String.sub text ~pos ~len in
+    (* if we reconstructed [~f:ignore] or [?f:ignore], we should take only
+       [ignore], so: *)
+    if
+      String.is_prefix reconstructed_prefix ~prefix:"~"
+      || String.is_prefix reconstructed_prefix ~prefix:"?"
+    then
+      match String.lsplit2 reconstructed_prefix ~on:':' with
+      | Some (_, s) -> s
+      | None -> reconstructed_prefix
+    else
+      reconstructed_prefix
 
 let suffix_of_position source position =
   match Msource.text source with
diff --git a/ocaml-lsp-server/test/e2e/__tests__/textDocument-completion.test.ts b/ocaml-lsp-server/test/e2e/__tests__/textDocument-completion.test.ts
index 2a69eda65..ff3883fd3 100644
--- a/ocaml-lsp-server/test/e2e/__tests__/textDocument-completion.test.ts
+++ b/ocaml-lsp-server/test/e2e/__tests__/textDocument-completion.test.ts
@@ -77,6 +77,124 @@ describe_opt("textDocument/completion", () => {
     expect(items).toMatchObject([{ label: "StringLabels" }]);
   });
 
+  it("can complete symbol passed as a named argument", async () => {
+    await openDocument(outdent`
+let g ~f = f 0 in
+g ~f:ig
+    `);
+
+    let items = await queryCompletion(Types.Position.create(1, 7));
+    expect(items).toMatchInlineSnapshot(`
+      Array [
+        Object {
+          "label": "ignore",
+          "textEdit": Object {
+            "newText": "ignore",
+            "range": Object {
+              "end": Object {
+                "character": 7,
+                "line": 1,
+              },
+              "start": Object {
+                "character": 5,
+                "line": 1,
+              },
+            },
+          },
+        },
+      ]
+    `);
+  });
+
+  it("can complete symbol passed as a named argument - 2", async () => {
+    await openDocument(outdent`
+module M = struct let igfoo _x = () end
+let g ~f = f 0 in
+g ~f:M.ig
+    `);
+
+    let items = await queryCompletion(Types.Position.create(2, 9));
+    expect(items).toMatchInlineSnapshot(`
+      Array [
+        Object {
+          "label": "igfoo",
+          "textEdit": Object {
+            "newText": "igfoo",
+            "range": Object {
+              "end": Object {
+                "character": 9,
+                "line": 2,
+              },
+              "start": Object {
+                "character": 7,
+                "line": 2,
+              },
+            },
+          },
+        },
+      ]
+    `);
+  });
+
+  it("can complete symbol passed as an optional argument", async () => {
+    await openDocument(outdent`
+let g ?f = f in
+g ?f:ig
+    `);
+
+    let items = await queryCompletion(Types.Position.create(1, 7));
+    expect(items).toMatchInlineSnapshot(`
+      Array [
+        Object {
+          "label": "ignore",
+          "textEdit": Object {
+            "newText": "ignore",
+            "range": Object {
+              "end": Object {
+                "character": 7,
+                "line": 1,
+              },
+              "start": Object {
+                "character": 5,
+                "line": 1,
+              },
+            },
+          },
+        },
+      ]
+    `);
+  });
+
+  it("can complete symbol passed as a optional argument - 2", async () => {
+    await openDocument(outdent`
+module M = struct let igfoo _x = () end
+let g ?f = f in
+g ?f:M.ig
+    `);
+
+    let items = await queryCompletion(Types.Position.create(2, 9));
+    expect(items).toMatchInlineSnapshot(`
+      Array [
+        Object {
+          "label": "igfoo",
+          "textEdit": Object {
+            "newText": "igfoo",
+            "range": Object {
+              "end": Object {
+                "character": 9,
+                "line": 2,
+              },
+              "start": Object {
+                "character": 7,
+                "line": 2,
+              },
+            },
+          },
+        },
+      ]
+    `);
+  });
+
   it("completes identifier at top level", async () => {
     await openDocument(outdent`
       let somenum = 42