diff --git a/changelog_unreleased/typescript/18852.md b/changelog_unreleased/typescript/18852.md
new file mode 100644
index 000000000..fea605600
--- /dev/null
+++ b/changelog_unreleased/typescript/18852.md
@@ -0,0 +1,35 @@
+#### Fix required semicolon in `no-semi` mode (#18852 by @fisker)
+
+<!-- prettier-ignore -->
+```tsx
+// Input
+declare module "autoprefixer";
+{
+  alert()
+}
+declare function a();
+{
+  alert()
+}
+
+// Prettier stable (--no-semi)
+declare module "autoprefixer"
+{
+  alert()
+}
+declare function a()
+{
+  alert()
+}
+
+
+// Prettier main (--no-semi)
+declare module "autoprefixer";
+{
+  alert();
+}
+declare function a();
+{
+  alert();
+}
+```
diff --git a/src/language-js/print/function.js b/src/language-js/print/function.js
index 42fc7e89e..03241c8be 100644
--- a/src/language-js/print/function.js
+++ b/src/language-js/print/function.js
@@ -84,9 +84,11 @@ function printFunction(path, options, print, args) {
       shouldGroupParameters ? group(parametersDoc) : parametersDoc,
       returnTypeDoc,
     ]),
-    node.body ? " " : "",
-    print("body"),
-    node.declare || !node.body ? printSemicolon(options) : "",
+    node.body
+      ? [" ", print("body")]
+      : // The semicolon not always needed,
+        // but prevent block statement after been parsed as body
+        ";",
   ];
 }
 
diff --git a/src/language-js/print/module-declaration.js b/src/language-js/print/module-declaration.js
index 162c1e357..e93927915 100644
--- a/src/language-js/print/module-declaration.js
+++ b/src/language-js/print/module-declaration.js
@@ -1,5 +1,5 @@
 import { group } from "../../document/index.js";
-import { printDeclareToken, printSemicolon } from "./miscellaneous.js";
+import { printDeclareToken } from "./miscellaneous.js";
 
 /*
 - `TSModuleDeclaration` (TypeScript)
@@ -11,7 +11,11 @@ function printModuleDeclaration(path, options, print) {
     printDeclareToken(path),
     node.kind === "global" ? "" : `${node.kind} `,
     print("id"),
-    node.body ? [" ", group(print("body"))] : printSemicolon(options),
+    node.body
+      ? [" ", group(print("body"))]
+      : // The semicolon not always needed,
+        // but prevent block statement after been parsed as body
+        ";",
   ];
 }
 
diff --git a/tests/format/flow/no-semi/asi/__snapshots__/format.test.js.snap b/tests/format/flow/no-semi/asi/__snapshots__/format.test.js.snap
new file mode 100644
index 000000000..c1441442e
--- /dev/null
+++ b/tests/format/flow/no-semi/asi/__snapshots__/format.test.js.snap
@@ -0,0 +1,35 @@
+// Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
+
+exports[`no-semi.js - {"semi":false} format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+semi: false
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+declare function foo():void;
+
+{
+  foo
+}
+
+declare hook foo(): Foo;
+
+{
+  foo
+}
+
+=====================================output=====================================
+declare function foo(): void
+
+{
+  foo
+}
+
+declare hook foo(): Foo
+
+{
+  foo
+}
+
+================================================================================
+`;
diff --git a/tests/format/flow/no-semi/asi/format.test.js b/tests/format/flow/no-semi/asi/format.test.js
new file mode 100644
index 000000000..54c60c57c
--- /dev/null
+++ b/tests/format/flow/no-semi/asi/format.test.js
@@ -0,0 +1 @@
+runFormatTest(import.meta, ["flow"], { semi: false });
diff --git a/tests/format/flow/no-semi/asi/no-semi.js b/tests/format/flow/no-semi/asi/no-semi.js
new file mode 100644
index 000000000..53dc8479b
--- /dev/null
+++ b/tests/format/flow/no-semi/asi/no-semi.js
@@ -0,0 +1,11 @@
+declare function foo():void;
+
+{
+  foo
+}
+
+declare hook foo(): Foo;
+
+{
+  foo
+}
diff --git a/tests/format/typescript/nosemi/__snapshots__/format.test.js.snap b/tests/format/typescript/nosemi/__snapshots__/format.test.js.snap
index 8f1770d2a..d69d486de 100644
--- a/tests/format/typescript/nosemi/__snapshots__/format.test.js.snap
+++ b/tests/format/typescript/nosemi/__snapshots__/format.test.js.snap
@@ -1,5 +1,44 @@
 // Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
+exports[`functions.ts - {"semi":false} format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+semi: false
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+declare function a():void;
+
+{
+  foo()
+}
+
+
+declare function b():void;
+
+[foo()]
+
+
+for(;;) function c();
+{}
+
+=====================================output=====================================
+declare function a(): void;
+
+{
+  foo()
+}
+
+declare function b(): void;
+
+;[foo()]
+
+for (;;) function c();
+{
+}
+
+================================================================================
+`;
+
 exports[`index-signature.ts - {"semi":false} format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]
@@ -53,6 +92,48 @@ interface InlineMultiple {
 ================================================================================
 `;
 
+exports[`module-declaration.ts - {"semi":false} format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+semi: false
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+declare module "foo";
+
+{
+  foo()
+}
+
+declare module "bar" {};
+
+{
+  foo()
+}
+
+declare module "baz";
+
+[foo()]
+
+=====================================output=====================================
+declare module "foo";
+
+{
+  foo()
+}
+
+declare module "bar" {}
+
+{
+  foo()
+}
+
+declare module "baz";
+
+;[foo()]
+
+================================================================================
+`;
+
 exports[`type.ts - {"semi":false} format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]
diff --git a/tests/format/typescript/nosemi/functions.ts b/tests/format/typescript/nosemi/functions.ts
new file mode 100644
index 000000000..b15c792ff
--- /dev/null
+++ b/tests/format/typescript/nosemi/functions.ts
@@ -0,0 +1,14 @@
+declare function a():void;
+
+{
+  foo()
+}
+
+
+declare function b():void;
+
+[foo()]
+
+
+for(;;) function c();
+{}
diff --git a/tests/format/typescript/nosemi/module-declaration.ts b/tests/format/typescript/nosemi/module-declaration.ts
new file mode 100644
index 000000000..29f92b9c1
--- /dev/null
+++ b/tests/format/typescript/nosemi/module-declaration.ts
@@ -0,0 +1,15 @@
+declare module "foo";
+
+{
+  foo()
+}
+
+declare module "bar" {};
+
+{
+  foo()
+}
+
+declare module "baz";
+
+[foo()]