@@ -31161,6 +31161,8 @@ func (c *Checker) newSetterFunctionType(t *Type) *Type {
 
 // Creates a synthetic `Signature` corresponding to a call signature.
 func (c *Checker) newCallSignature(typeParameters []*Type, thisParameter *ast.Symbol, parameters []*ast.Symbol, returnType *Type) *Signature {
+	// The shared declaration supplies syntax and source-file identity only;
+	// parameter and return types are stored on the signature.
 	decl := GetSyntheticSignatureSourceFile().Statements.Nodes[0].Type()
 	return c.newSignature(SignatureFlagsNone, decl, typeParameters, thisParameter, parameters, returnType, nil, len(parameters))
 }
 
@@ -12,10 +12,16 @@ import (
 const SyntheticSignatureFileName tspath.RootedFilePath = "tsgo://synthetic/signatures.d.ts"
 
 var syntheticSignatureSourceFile = sync.OnceValue(func() *ast.SourceFile {
-	return parser.ParseSourceFile(ast.SourceFileParseOptions{
+	file := parser.ParseSourceFile(ast.SourceFileParseOptions{
 		FileName: SyntheticSignatureFileName,
 		PathKey:  tspath.CaseSensitive.PathKey(tspath.RootedPath(SyntheticSignatureFileName)),
 	}, "type SyntheticSignature = () => any;", core.ScriptKindTS)
+	// Keep the placeholder synthesized so declaration serialization uses the
+	// signature's types rather than treating this as a bound source declaration.
+	declaration := file.Statements.Nodes[0].Type()
+	declaration.Loc = core.UndefinedTextRange()
+	declaration.Type().Loc = core.UndefinedTextRange()
+	return file
 })
 
 // GetSyntheticSignatureSourceFile provides an immutable, shared AST for synthetic
Original file line number	Diff line number	Diff line change
`@@ -31161,6 +31161,8 @@ func (c Checker) newSetterFunctionType(t Type) *Type {`
`31161`	`31161`
`31162`	`31162`	// Creates a synthetic `Signature` corresponding to a call signature.
`31163`	`31163`	`func (c Checker) newCallSignature(typeParameters []Type, thisParameter ast.Symbol, parameters []ast.Symbol, returnType Type) Signature {`
	`31164`	`+ // The shared declaration supplies syntax and source-file identity only;`
	`31165`	`+ // parameter and return types are stored on the signature.`
`31164`	`31166`	`decl := GetSyntheticSignatureSourceFile().Statements.Nodes[0].Type()`
`31165`	`31167`	`return c.newSignature(SignatureFlagsNone, decl, typeParameters, thisParameter, parameters, returnType, nil, len(parameters))`
`31166`	`31168`	`}`