diff --git a/src/parser/expression.js b/src/parser/expression.js
index df90d47f0a..0c435bb64a 100644
--- a/src/parser/expression.js
+++ b/src/parser/expression.js
@@ -343,7 +343,7 @@ pp.parseCallExpressionArguments = function (close, possibleAsyncArrow) {
       innerParenStart = this.state.start;
     }
 
-    elts.push(this.parseExprListItem(undefined, possibleAsyncArrow ? { start: 0 } : undefined));
+    elts.push(this.parseExprListItem(false, possibleAsyncArrow ? { start: 0 } : undefined, possibleAsyncArrow ? { start: 0 } : undefined));
   }
 
   // we found an async arrow function so let's not allow any inner parens
@@ -1021,14 +1021,14 @@ pp.parseExprList = function (close, allowEmpty, refShorthandDefaultPos) {
   return elts;
 };
 
-pp.parseExprListItem = function (allowEmpty, refShorthandDefaultPos) {
+pp.parseExprListItem = function (allowEmpty, refShorthandDefaultPos, refNeedsArrowPos) {
   let elt;
   if (allowEmpty && this.match(tt.comma)) {
     elt = null;
   } else if (this.match(tt.ellipsis)) {
     elt = this.parseSpread(refShorthandDefaultPos);
   } else {
-    elt = this.parseMaybeAssign(false, refShorthandDefaultPos, this.parseParenItem);
+    elt = this.parseMaybeAssign(false, refShorthandDefaultPos, this.parseParenItem, refNeedsArrowPos);
   }
   return elt;
 };
diff --git a/src/plugins/flow.js b/src/plugins/flow.js
index 8927bed198..04ea9527ac 100644
--- a/src/plugins/flow.js
+++ b/src/plugins/flow.js
@@ -1041,9 +1041,9 @@ export default function (instance) {
   // parse an item inside a expression list eg. `(NODE, NODE)` where NODE represents
   // the position where this function is called
   instance.extend("parseExprListItem", function (inner) {
-    return function (allowEmpty, refShorthandDefaultPos) {
+    return function (...args) {
       const container = this.startNode();
-      const node = inner.call(this, allowEmpty, refShorthandDefaultPos);
+      const node = inner.call(this, ...args);
       if (this.match(tt.colon)) {
         container._exprListItem = true;
         container.expression = node;
diff --git a/test/fixtures/flow/regression/issue-336/actual.js b/test/fixtures/flow/regression/issue-336/actual.js
new file mode 100644
index 0000000000..aa55e12462
--- /dev/null
+++ b/test/fixtures/flow/regression/issue-336/actual.js
@@ -0,0 +1 @@
+const fn = async (a?: any): Promise<void> => {};
diff --git a/test/fixtures/flow/regression/issue-336/expected.json b/test/fixtures/flow/regression/issue-336/expected.json
new file mode 100644
index 0000000000..3c169bcd54
--- /dev/null
+++ b/test/fixtures/flow/regression/issue-336/expected.json
@@ -0,0 +1,249 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 48,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 48
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 48,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 48
+      }
+    },
+    "sourceType": "module",
+    "body": [
+      {
+        "type": "VariableDeclaration",
+        "start": 0,
+        "end": 48,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 48
+          }
+        },
+        "declarations": [
+          {
+            "type": "VariableDeclarator",
+            "start": 6,
+            "end": 47,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 6
+              },
+              "end": {
+                "line": 1,
+                "column": 47
+              }
+            },
+            "id": {
+              "type": "Identifier",
+              "start": 6,
+              "end": 8,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 6
+                },
+                "end": {
+                  "line": 1,
+                  "column": 8
+                },
+                "identifierName": "fn"
+              },
+              "name": "fn"
+            },
+            "init": {
+              "type": "ArrowFunctionExpression",
+              "start": 11,
+              "end": 47,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 11
+                },
+                "end": {
+                  "line": 1,
+                  "column": 47
+                }
+              },
+              "returnType": {
+                "type": "TypeAnnotation",
+                "start": 26,
+                "end": 41,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 26
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 41
+                  }
+                },
+                "typeAnnotation": {
+                  "type": "GenericTypeAnnotation",
+                  "start": 28,
+                  "end": 41,
+                  "loc": {
+                    "start": {
+                      "line": 1,
+                      "column": 28
+                    },
+                    "end": {
+                      "line": 1,
+                      "column": 41
+                    }
+                  },
+                  "typeParameters": {
+                    "type": "TypeParameterInstantiation",
+                    "start": 35,
+                    "end": 41,
+                    "loc": {
+                      "start": {
+                        "line": 1,
+                        "column": 35
+                      },
+                      "end": {
+                        "line": 1,
+                        "column": 41
+                      }
+                    },
+                    "params": [
+                      {
+                        "type": "VoidTypeAnnotation",
+                        "start": 36,
+                        "end": 40,
+                        "loc": {
+                          "start": {
+                            "line": 1,
+                            "column": 36
+                          },
+                          "end": {
+                            "line": 1,
+                            "column": 40
+                          }
+                        }
+                      }
+                    ]
+                  },
+                  "id": {
+                    "type": "Identifier",
+                    "start": 28,
+                    "end": 35,
+                    "loc": {
+                      "start": {
+                        "line": 1,
+                        "column": 28
+                      },
+                      "end": {
+                        "line": 1,
+                        "column": 35
+                      },
+                      "identifierName": "Promise"
+                    },
+                    "name": "Promise"
+                  }
+                }
+              },
+              "id": null,
+              "generator": false,
+              "expression": false,
+              "async": true,
+              "params": [
+                {
+                  "type": "Identifier",
+                  "start": 18,
+                  "end": 25,
+                  "loc": {
+                    "start": {
+                      "line": 1,
+                      "column": 18
+                    },
+                    "end": {
+                      "line": 1,
+                      "column": 25
+                    },
+                    "identifierName": "a"
+                  },
+                  "name": "a",
+                  "optional": true,
+                  "typeAnnotation": {
+                    "type": "TypeAnnotation",
+                    "start": 20,
+                    "end": 25,
+                    "loc": {
+                      "start": {
+                        "line": 1,
+                        "column": 20
+                      },
+                      "end": {
+                        "line": 1,
+                        "column": 25
+                      }
+                    },
+                    "typeAnnotation": {
+                      "type": "AnyTypeAnnotation",
+                      "start": 22,
+                      "end": 25,
+                      "loc": {
+                        "start": {
+                          "line": 1,
+                          "column": 22
+                        },
+                        "end": {
+                          "line": 1,
+                          "column": 25
+                        }
+                      }
+                    }
+                  }
+                }
+              ],
+              "body": {
+                "type": "BlockStatement",
+                "start": 45,
+                "end": 47,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 45
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 47
+                  }
+                },
+                "body": [],
+                "directives": []
+              }
+            }
+          }
+        ],
+        "kind": "const"
+      }
+    ],
+    "directives": []
+  }
+}
\ No newline at end of file