diff --git a/internal/transformers/declarations/transform.go b/internal/transformers/declarations/transform.go
index 07ff921521..02bb0d9d41 100644
--- a/internal/transformers/declarations/transform.go
+++ b/internal/transformers/declarations/transform.go
@@ -741,11 +741,16 @@ func (tx *DeclarationTransformer) transformPropertyDeclaration(input *ast.Proper
 	if ast.IsPrivateIdentifier(input.Name()) {
 		return nil
 	}
+	// Remove definite assignment assertion (!) from declaration files
+	postfixToken := input.PostfixToken
+	if postfixToken != nil && postfixToken.Kind == ast.KindExclamationToken {
+		postfixToken = nil
+	}
 	return tx.Factory().UpdatePropertyDeclaration(
 		input,
 		tx.ensureModifiers(input.AsNode()),
 		input.Name(),
-		input.PostfixToken,
+		postfixToken,
 		tx.ensureType(input.AsNode(), false),
 		tx.ensureNoInitializer(input.AsNode()),
 	)
diff --git a/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js b/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js
index 513675497e..35209340b0 100644
--- a/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js
+++ b/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js
@@ -15,25 +15,6 @@ class Foo {
 
 //// [declarationEmitTypeofThisInClass.d.ts]
 declare class Foo {
-    foo!: string;
-    bar!: typeof this.foo; //Public property 'bar' of exported class has or is using private name 'this'.(4031)
+    foo: string;
+    bar: typeof this.foo; //Public property 'bar' of exported class has or is using private name 'this'.(4031)
 }
-
-
-//// [DtsFileErrors]
-
-
-declarationEmitTypeofThisInClass.d.ts(2,8): error TS1255: A definite assignment assertion '!' is not permitted in this context.
-declarationEmitTypeofThisInClass.d.ts(3,8): error TS1255: A definite assignment assertion '!' is not permitted in this context.
-
-
-==== declarationEmitTypeofThisInClass.d.ts (2 errors) ====
-    declare class Foo {
-        foo!: string;
-           ~
-!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
-        bar!: typeof this.foo; //Public property 'bar' of exported class has or is using private name 'this'.(4031)
-           ~
-!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
-    }
-    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js.diff b/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js.diff
index fd7f466383..4986e2b51c 100644
--- a/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js.diff
+++ b/testdata/baselines/reference/submodule/compiler/declarationEmitTypeofThisInClass.js.diff
@@ -13,27 +13,7 @@
 
  //// [declarationEmitTypeofThisInClass.d.ts]
  declare class Foo {
--    foo: string;
+     foo: string;
 -    bar: typeof this.foo;
-+    foo!: string;
-+    bar!: typeof this.foo; //Public property 'bar' of exported class has or is using private name 'this'.(4031)
- }
-+
-+
-+//// [DtsFileErrors]
-+
-+
-+declarationEmitTypeofThisInClass.d.ts(2,8): error TS1255: A definite assignment assertion '!' is not permitted in this context.
-+declarationEmitTypeofThisInClass.d.ts(3,8): error TS1255: A definite assignment assertion '!' is not permitted in this context.
-+
-+
-+==== declarationEmitTypeofThisInClass.d.ts (2 errors) ====
-+    declare class Foo {
-+        foo!: string;
-+           ~
-+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
-+        bar!: typeof this.foo; //Public property 'bar' of exported class has or is using private name 'this'.(4031)
-+           ~
-+!!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
-+    }
-+    
\ No newline at end of file
++    bar: typeof this.foo; //Public property 'bar' of exported class has or is using private name 'this'.(4031)
+ }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js b/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js
index 708b5b22f8..99824f7bfa 100644
--- a/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js
+++ b/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js
@@ -77,7 +77,7 @@ declare class B extends A {
     x: number;
 }
 declare class C {
-    a!: number;
+    a: number;
     b: number;
 }
 // Repro from #37979
diff --git a/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js.diff b/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js.diff
index deddbe076d..3815821550 100644
--- a/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js.diff
+++ b/testdata/baselines/reference/submodule/compiler/initializerWithThisPropertyAccess.js.diff
@@ -56,12 +56,8 @@
      c: () => number;
      d: number;
      constructor();
-@@= skipped -46, +41 lines =@@
-     x: number;
- }
- declare class C {
--    a: number;
-+    a!: number;
+@@= skipped -49, +44 lines =@@
+     a: number;
      b: number;
  }
 +// Repro from #37979
diff --git a/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js b/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js
index 6693863b4c..13029babed 100644
--- a/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js
+++ b/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js
@@ -143,28 +143,28 @@ function f4() {
 //// [definiteAssignmentAssertions.d.ts]
 // Suppress strict property initialization check
 declare class C1 {
-    a!: number;
+    a: number;
     b: string; // Error
 }
 // Suppress definite assignment check in constructor
 declare class C2 {
-    a!: number;
+    a: number;
     constructor();
 }
 // Definite assignment assertion requires type annotation, no initializer, no static modifier
 declare class C3 {
-    a!: number;
-    b!: number;
-    static c!: number;
-    d!: any;
+    a: number;
+    b: number;
+    static c: number;
+    d: any;
 }
 // Definite assignment assertion not permitted in ambient context
 declare class C4 {
-    a!: number;
+    a: number;
 }
 // Definite assignment assertion not permitted on abstract property
 declare abstract class C5 {
-    abstract a!: number;
+    abstract a: number;
 }
 // Suppress definite assignment check for variable
 declare function f1(): void;
diff --git a/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js.diff b/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js.diff
index fe69e1efc0..ad6b1a8640 100644
--- a/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js.diff
+++ b/testdata/baselines/reference/submodule/conformance/definiteAssignmentAssertions.js.diff
@@ -40,37 +40,29 @@
  //// [definiteAssignmentAssertions.d.ts]
 +// Suppress strict property initialization check
  declare class C1 {
--    a: number;
+     a: number;
 -    b: string;
-+    a!: number;
 +    b: string; // Error
  }
 +// Suppress definite assignment check in constructor
  declare class C2 {
--    a: number;
-+    a!: number;
+     a: number;
      constructor();
  }
 +// Definite assignment assertion requires type annotation, no initializer, no static modifier
  declare class C3 {
--    a: number;
--    b: number;
--    static c: number;
--    d: any;
-+    a!: number;
-+    b!: number;
-+    static c!: number;
-+    d!: any;
+     a: number;
+     b: number;
+     static c: number;
+     d: any;
  }
 +// Definite assignment assertion not permitted in ambient context
  declare class C4 {
--    a: number;
-+    a!: number;
+     a: number;
  }
 +// Definite assignment assertion not permitted on abstract property
  declare abstract class C5 {
--    abstract a: number;
-+    abstract a!: number;
+     abstract a: number;
  }
 +// Suppress definite assignment check for variable
  declare function f1(): void;
diff --git a/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js b/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js
index 99a3a5b35c..cc1037f80e 100644
--- a/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js
+++ b/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js
@@ -40,7 +40,7 @@ void type; // Ok
 
 //// [a.d.ts]
 declare class A {
-    a!: string;
+    a: string;
 }
 export = A;
 //// [b.d.ts]
diff --git a/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js.diff b/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js.diff
index bd64ec0e30..639e20e004 100644
--- a/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js.diff
+++ b/testdata/baselines/reference/submodule/conformance/importEqualsDeclaration.js.diff
@@ -17,16 +17,7 @@
  A.prototype; // Error
  const a = { a: 'a' }; // Ok
  void type; // Ok
-@@= skipped -8, +8 lines =@@
-
- //// [a.d.ts]
- declare class A {
--    a: string;
-+    a!: string;
- }
- export = A;
- //// [b.d.ts]
-@@= skipped -8, +8 lines =@@
+@@= skipped -16, +16 lines =@@
  }
  export = SomeClass;
  //// [c.d.ts]