diff --git a/blocks_runtime.m b/blocks_runtime.m
index 3a78461..7be65c9 100644
--- a/blocks_runtime.m
+++ b/blocks_runtime.m
@@ -39,7 +39,7 @@
 static void *_HeapBlockByRef = (void*)1;
 
 
-OBJC_PUBLIC _Bool _Block_has_signature(id b)
+OBJC_PUBLIC bool _Block_has_signature(void *b)
 {
 	const struct Block_layout *block = (struct Block_layout*)b;
 	return ((NULL != block) && (block->flags & BLOCK_HAS_SIGNATURE));
@@ -47,7 +47,7 @@ OBJC_PUBLIC _Bool _Block_has_signature(id b)
 /**
  * Returns the Objective-C type encoding for the block.
  */
-OBJC_PUBLIC const char * _Block_signature(id b)
+OBJC_PUBLIC const char * _Block_signature(void *b)
 {
 	const struct Block_layout *block = (struct Block_layout*)b;
 	if ((NULL == block) || !(block->flags & BLOCK_HAS_SIGNATURE))
diff --git a/objc/blocks_runtime.h b/objc/blocks_runtime.h
index c20564e..7a9d23f 100644
--- a/objc/blocks_runtime.h
+++ b/objc/blocks_runtime.h
@@ -7,22 +7,19 @@
  * Blocks Runtime
  */
 #include "Availability.h"
+#include <stdbool.h>
 #ifdef __cplusplus
-#define OBJC_BOOL_TYPE bool
-#define OBJC_BLOCK_PTR_TYPE void*
 #define BLOCKS_EXPORT extern "C"
 #else
-#define OBJC_BOOL_TYPE _Bool
-#define OBJC_BLOCK_PTR_TYPE id
-#define BLOCKS_EXPORT extern 
+#define BLOCKS_EXPORT extern
 #endif
 
 OBJC_PUBLIC BLOCKS_EXPORT void *_Block_copy(const void *);
 OBJC_PUBLIC BLOCKS_EXPORT void _Block_release(const void *);
 OBJC_PUBLIC BLOCKS_EXPORT const char *block_getType_np(const void *b) OBJC_NONPORTABLE;
 
-OBJC_PUBLIC BLOCKS_EXPORT OBJC_BOOL_TYPE _Block_has_signature(OBJC_BLOCK_PTR_TYPE);
-OBJC_PUBLIC BLOCKS_EXPORT const char * _Block_signature(OBJC_BLOCK_PTR_TYPE);
+OBJC_PUBLIC BLOCKS_EXPORT bool _Block_has_signature(void *);
+OBJC_PUBLIC BLOCKS_EXPORT const char * _Block_signature(void *);
 
 
 #define Block_copy(x) ((__typeof(x))_Block_copy((const void *)(x)))