--- a/xpcom/typelib/xpt/xpt_arena.h
+++ b/xpcom/typelib/xpt/xpt_arena.h
@@ -10,25 +10,21 @@
 #ifndef __xpt_arena_h__
 #define __xpt_arena_h__
 
 #include <stdlib.h>
 #include "mozilla/Attributes.h"
 #include "mozilla/MemoryReporting.h"
 #include <stdint.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /*
  * Simple Arena support. Use with caution!
  */
 
-typedef struct XPTArena XPTArena;
+struct XPTArena;
 
 XPTArena*
 XPT_NewArena(size_t block_size8, size_t block_size1);
 
 void
 XPT_DestroyArena(XPTArena *arena);
 
 void*
@@ -50,13 +46,9 @@ void
 XPT_AssertFailed(const char *s, const char *file, uint32_t lineno)
   MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS;
 #define XPT_ASSERT(_expr) \
     ((_expr)?((void)0):XPT_AssertFailed(# _expr, __FILE__, __LINE__))
 #else
 #define XPT_ASSERT(_expr) ((void)0)
 #endif
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* __xpt_arena_h__ */

--- a/xpcom/typelib/xpt/xpt_struct.h
+++ b/xpcom/typelib/xpt/xpt_struct.h
@@ -9,37 +9,35 @@
  */
 
 #ifndef __xpt_struct_h__
 #define __xpt_struct_h__
 
 #include "xpt_arena.h"
 #include <stdint.h>
 
-extern "C" {
-
 /*
  * Originally, I was going to have structures that exactly matched the on-disk
  * representation, but that proved difficult: different compilers can pack
  * their structs differently, and that makes overlaying them atop a
  * read-from-disk byte buffer troublesome.  So now I just have some structures
  * that are used in memory, and we're going to write a nice XDR library to
  * write them to disk and stuff.  It is pure joy. -- shaver
  */
 
 /* Structures for the typelib components */
 
-typedef struct XPTHeader XPTHeader;
-typedef struct XPTInterfaceDirectoryEntry XPTInterfaceDirectoryEntry;
-typedef struct XPTInterfaceDescriptor XPTInterfaceDescriptor;
-typedef struct XPTConstDescriptor XPTConstDescriptor;
-typedef struct XPTMethodDescriptor XPTMethodDescriptor;
-typedef struct XPTParamDescriptor XPTParamDescriptor;
-typedef struct XPTTypeDescriptor XPTTypeDescriptor;
-typedef struct XPTTypeDescriptorPrefix XPTTypeDescriptorPrefix;
+struct XPTHeader;
+struct XPTInterfaceDirectoryEntry;
+struct XPTInterfaceDescriptor;
+struct XPTConstDescriptor;
+struct XPTMethodDescriptor;
+struct XPTParamDescriptor;
+struct XPTTypeDescriptor;
+struct XPTTypeDescriptorPrefix;
 
 #ifndef nsID_h__
 /*
  * We can't include nsID.h, because it's full of C++ goop and we're not doing
  * C++ here, so we define our own minimal struct.  We protect against multiple
  * definitions of this struct, though, and use the same field naming.
  */
 struct nsID {
@@ -351,16 +349,14 @@ struct XPTMethodDescriptor {
  * EmptyAnnotation. EmptyAnnotation's are ignored - they're only used to
  * indicate an array of Annotation's that's completely empty.  If the tag
  * is 1, the record is a PrivateAnnotation.
  *
  * We don't actually store annotations; we just skip over them if they are
  * present.
  */
 
-#define XPT_ANN_LAST	                0x80
+#define XPT_ANN_LAST                    0x80
 #define XPT_ANN_IS_LAST(flags)          (flags & XPT_ANN_LAST)
 #define XPT_ANN_PRIVATE                 0x40
 #define XPT_ANN_IS_PRIVATE(flags)       (flags & XPT_ANN_PRIVATE)
 
-}
-
 #endif /* __xpt_struct_h__ */

--- a/xpcom/typelib/xpt/xpt_xdr.h
+++ b/xpcom/typelib/xpt/xpt_xdr.h
@@ -10,22 +10,18 @@
 #ifndef __xpt_xdr_h__
 #define __xpt_xdr_h__
 
 #include "xpt_struct.h"
 #include "mozilla/NotNull.h"
 
 using mozilla::NotNull;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-typedef struct XPTState         XPTState;
-typedef struct XPTCursor        XPTCursor;
+struct XPTState;
+struct XPTCursor;
 
 bool
 XPT_SkipStringInline(NotNull<XPTCursor*> cursor);
 
 bool
 XPT_DoCString(XPTArena *arena, NotNull<XPTCursor*> cursor, char **strp,
               bool ignore = false);
 
@@ -42,20 +38,20 @@ bool
 XPT_Do16(NotNull<XPTCursor*> cursor, uint16_t *u16p);
 
 bool
 XPT_Do8(NotNull<XPTCursor*> cursor, uint8_t *u8p);
 
 bool
 XPT_DoHeader(XPTArena *arena, NotNull<XPTCursor*> cursor, XPTHeader **headerp);
 
-typedef enum {
+enum XPTPool {
     XPT_HEADER = 0,
     XPT_DATA = 1
-} XPTPool;
+};
 
 struct XPTState {
     uint32_t         data_offset;
     uint32_t         next_cursor[2];
     char             *pool_data;
     uint32_t         pool_allocated;
 };
 
@@ -74,13 +70,9 @@ XPT_MakeCursor(XPTState *state, XPTPool 
                NotNull<XPTCursor*> cursor);
 
 bool
 XPT_SeekTo(NotNull<XPTCursor*> cursor, uint32_t offset);
 
 void
 XPT_SetDataOffset(XPTState *state, uint32_t data_offset);
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* __xpt_xdr_h__ */