diff --git a/changelog_unreleased/typescript/10457.md b/changelog_unreleased/typescript/10457.md
new file mode 100644
index 000000000000..8587da5a2472
--- /dev/null
+++ b/changelog_unreleased/typescript/10457.md
@@ -0,0 +1,13 @@
+#### Fix misplaced comments in unions and intersections (#10457 by @thorn0)
+
+<!-- prettier-ignore -->
+```ts
+// Input
+type Foo = "1" | "2" /* two */ | "3";
+
+// Prettier stable
+type Foo = "1" | "2" | /* two */ "3";
+
+// Prettier main
+type Foo = "1" | "2" /* two */ | "3";
+```
diff --git a/src/language-js/clean.js b/src/language-js/clean.js
index 60be0872ff59..903988eb6f72 100644
--- a/src/language-js/clean.js
+++ b/src/language-js/clean.js
@@ -197,6 +197,14 @@ function clean(ast, newObj, parent) {
   if (ast.type === "InterpreterDirective") {
     newObj.value = newObj.value.trimEnd();
   }
+
+  // Prettier removes degenerate union and intersection types with only one member.
+  if (
+    (ast.type === "TSIntersectionType" || ast.type === "TSUnionType") &&
+    ast.types.length === 1
+  ) {
+    return newObj.types[0];
+  }
 }
 
 clean.ignoredProperties = ignoredProperties;
diff --git a/src/language-js/comments.js b/src/language-js/comments.js
index 944672998ec6..d40b113e4fd3 100644
--- a/src/language-js/comments.js
+++ b/src/language-js/comments.js
@@ -886,22 +886,6 @@ function isRealFunctionLikeNode(node) {
   );
 }
 
-/**
- * @param {Node} enclosingNode
- * @returns {RegExp | void}
- */
-function getGapRegex(enclosingNode) {
-  if (
-    enclosingNode &&
-    enclosingNode.type !== "BinaryExpression" &&
-    enclosingNode.type !== "LogicalExpression"
-  ) {
-    // Support degenerate single-element unions and intersections.
-    // E.g.: `type A = /* 1 */ & B`
-    return /^[\s&(|]*$/;
-  }
-}
-
 /**
  * @param {any} node
  * @returns {Node[] | void}
@@ -980,7 +964,6 @@ module.exports = {
   handleEndOfLineComment,
   handleRemainingComment,
   isTypeCastComment,
-  getGapRegex,
   getCommentChildNodes,
   willPrintOwnComments,
 };
diff --git a/src/language-js/needs-parens.js b/src/language-js/needs-parens.js
index 7a2fb10c809d..f897421e5b6e 100644
--- a/src/language-js/needs-parens.js
+++ b/src/language-js/needs-parens.js
@@ -405,8 +405,10 @@ function needsParens(path, options) {
     case "TSUnionType":
     case "TSIntersectionType":
       if (
-        parent.type === "TSUnionType" ||
-        parent.type === "TSIntersectionType"
+        (parent.type === "TSUnionType" ||
+          parent.type === "TSIntersectionType") &&
+        parent.types.length > 1 &&
+        (!node.types || node.types.length > 1)
       ) {
         return true;
       }
diff --git a/src/language-js/parse-postprocess.js b/src/language-js/parse-postprocess.js
index be9dcd9ddf42..2a9b4fbaeb58 100644
--- a/src/language-js/parse-postprocess.js
+++ b/src/language-js/parse-postprocess.js
@@ -129,15 +129,6 @@ function postprocess(ast, options) {
         node.typeAnnotation.range = [locStart(node), locEnd(node)];
         return node.typeAnnotation;
       }
-      case "TSUnionType":
-      case "TSIntersectionType":
-        if (node.types.length === 1) {
-          const [firstType] = node.types;
-          // override loc, so that comments are attached properly
-          firstType.range = [locStart(node), locEnd(node)];
-          return firstType;
-        }
-        break;
       case "TSTypeParameter":
         // babel-ts
         if (typeof node.name === "string") {
diff --git a/src/language-js/printer-estree.js b/src/language-js/printer-estree.js
index 502f5651d4d4..a12301870e43 100644
--- a/src/language-js/printer-estree.js
+++ b/src/language-js/printer-estree.js
@@ -1088,6 +1088,5 @@ module.exports = {
     endOfLine: handleComments.handleEndOfLineComment,
     remaining: handleComments.handleRemainingComment,
   },
-  getGapRegex: handleComments.getGapRegex,
   getCommentChildNodes: handleComments.getCommentChildNodes,
 };
diff --git a/tests/typescript/union/__snapshots__/jsfmt.spec.js.snap b/tests/typescript/union/__snapshots__/jsfmt.spec.js.snap
index 55a2716f71ee..3ab365a493df 100644
--- a/tests/typescript/union/__snapshots__/jsfmt.spec.js.snap
+++ b/tests/typescript/union/__snapshots__/jsfmt.spec.js.snap
@@ -1,5 +1,37 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`comments.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type A1 = a /* 1 */ | b;
+type A2 = a | /* 1 */ b;
+type A3 = (a /* 1 */) | b;
+type A4 = a | (/* 1 */ b);
+type A5 = (a) /* 1 */ | b;
+type A6 = a | /* 1 */ (b);
+
+type B1 = a /* 1 */ /* 2 */ | b;
+type B2 = a /* 1 */ | /* 2 */ b;
+type B3 = a | /* 1 */ /* 2 */ b;
+
+=====================================output=====================================
+type A1 = a /* 1 */ | b;
+type A2 = a | /* 1 */ b;
+type A3 = a /* 1 */ | b;
+type A4 = a | /* 1 */ b;
+type A5 = a /* 1 */ | b;
+type A6 = a | /* 1 */ b;
+
+type B1 = a /* 1 */ /* 2 */ | b;
+type B2 = a /* 1 */ | /* 2 */ b;
+type B3 = a | /* 1 */ /* 2 */ b;
+
+================================================================================
+`;
+
 exports[`inlining.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]
diff --git a/tests/typescript/union/comments.ts b/tests/typescript/union/comments.ts
new file mode 100644
index 000000000000..d3f32ddd12d9
--- /dev/null
+++ b/tests/typescript/union/comments.ts
@@ -0,0 +1,10 @@
+type A1 = a /* 1 */ | b;
+type A2 = a | /* 1 */ b;
+type A3 = (a /* 1 */) | b;
+type A4 = a | (/* 1 */ b);
+type A5 = (a) /* 1 */ | b;
+type A6 = a | /* 1 */ (b);
+
+type B1 = a /* 1 */ /* 2 */ | b;
+type B2 = a /* 1 */ | /* 2 */ b;
+type B3 = a | /* 1 */ /* 2 */ b;