diff --git a/include/swift-c/SyntaxParser/SwiftSyntaxCDataTypes.h b/include/swift-c/SyntaxParser/SwiftSyntaxCDataTypes.h
new file mode 100644
index 0000000000000..bb64edb9cb585
--- /dev/null
+++ b/include/swift-c/SyntaxParser/SwiftSyntaxCDataTypes.h
@@ -0,0 +1,76 @@
+//===------------------ SwiftSyntaxCDataTypes.h -------------------*- C -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+// There are two copies of this file in the Swift compiler repository and in  //
+// the SwiftSyntax repository. They need to always share the same contents.   //
+//                                                                            //
+// The reason behind this is that the SwiftSyntax module should be able to    //
+// build with no dependencies to the compiler repo (in particular not         //
+// _InternalSwiftSyntaxParser) so that it can be used for code generation     //
+// without a matching toolchain. But to make SwiftSyntax parsing efficient,   //
+// we need to create RawSyntax nodes from the C nodes without any conversion  //
+// and thus SwiftSyntax needs to have knowledge about the layout of these C   //
+// types. Thus the two copies of the file. The equality of these files is     //
+// checked in CI (verify the source matches) and at runtime by                //
+// SwiftSyntaxParser (verify that a hash generated from the layouts matches)  //
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_C_SYNTAX_C_DATA_TYPES_H
+#define SWIFT_C_SYNTAX_C_DATA_TYPES_H
+
+#include <stdbool.h>
+
+/// Offset+length in UTF8 bytes.
+typedef struct {
+  uint32_t offset;
+  uint32_t length;
+} swiftparse_range_t;
+
+typedef uint8_t swiftparse_trivia_kind_t;
+typedef uint8_t swiftparse_token_kind_t;
+typedef uint16_t swiftparse_syntax_kind_t;
+
+/// This is for the client to provide an opaque pointer that the parser will
+/// associate with a syntax node.
+typedef void *swiftparse_client_node_t;
+
+typedef struct {
+  /// The length in source this trivia piece occupies, in UTF8 bytes.
+  uint32_t length;
+  swiftparse_trivia_kind_t kind;
+} swiftparse_trivia_piece_t;
+
+typedef struct {
+  const swiftparse_trivia_piece_t *leading_trivia;
+  const swiftparse_trivia_piece_t *trailing_trivia;
+  uint16_t leading_trivia_count;
+  uint16_t trailing_trivia_count;
+  swiftparse_token_kind_t kind;
+  /// Represents the range for the node, including trivia.
+  swiftparse_range_t range;
+} swiftparse_token_data_t;
+
+typedef struct {
+  const swiftparse_client_node_t *nodes;
+  uint32_t nodes_count;
+} swiftparse_layout_data_t;
+
+typedef struct {
+  union {
+    swiftparse_token_data_t token_data;
+    swiftparse_layout_data_t layout_data;
+  };
+  /// The syntax kind. A value of '0' means this is a token node.
+  swiftparse_syntax_kind_t kind;
+  bool present;
+} swiftparse_syntax_node_t;
+
+#endif
diff --git a/include/swift-c/SyntaxParser/SwiftSyntaxParser.h b/include/swift-c/SyntaxParser/SwiftSyntaxParser.h
index fde4aefcf3ba4..3b62975346506 100644
--- a/include/swift-c/SyntaxParser/SwiftSyntaxParser.h
+++ b/include/swift-c/SyntaxParser/SwiftSyntaxParser.h
@@ -75,52 +75,7 @@
 
 SWIFTPARSE_BEGIN_DECLS
 
-//=== Syntax Data Types ---------------------------------------------------===//
-
-/// Offset+length in UTF8 bytes.
-typedef struct {
-  uint32_t offset;
-  uint32_t length;
-} swiftparse_range_t;
-
-typedef uint8_t swiftparse_trivia_kind_t;
-typedef uint8_t swiftparse_token_kind_t;
-typedef uint16_t swiftparse_syntax_kind_t;
-
-/// This is for the client to provide an opaque pointer that the parser will
-/// associate with a syntax node.
-typedef void *swiftparse_client_node_t;
-
-typedef struct {
-  /// The length in source this trivia piece occupies, in UTF8 bytes.
-  uint32_t length;
-  swiftparse_trivia_kind_t kind;
-} swiftparse_trivia_piece_t;
-
-typedef struct {
-  const swiftparse_trivia_piece_t *leading_trivia;
-  const swiftparse_trivia_piece_t *trailing_trivia;
-  uint16_t leading_trivia_count;
-  uint16_t trailing_trivia_count;
-  swiftparse_token_kind_t kind;
-  /// Represents the range for the node, including trivia.
-  swiftparse_range_t range;
-} swiftparse_token_data_t;
-
-typedef struct {
-  const swiftparse_client_node_t *nodes;
-  uint32_t nodes_count;
-} swiftparse_layout_data_t;
-
-typedef struct {
-  union {
-    swiftparse_token_data_t token_data;
-    swiftparse_layout_data_t layout_data;
-  };
-  /// The syntax kind. A value of '0' means this is a token node.
-  swiftparse_syntax_kind_t kind;
-  bool present;
-} swiftparse_syntax_node_t;
+#include "SwiftSyntaxCDataTypes.h"
 
 //=== Parser Functions ----------------------------------------------------===//