diff --git a/mem.c b/mem.c
index 8c27491..1431264 100644
--- a/mem.c
+++ b/mem.c
@@ -8,8 +8,8 @@
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
-#define XC_SHM_IMPL
-#define XC_MEM_IMPL
+#define XC_MEMBLOCK_IMPL _xc_mem_block_t
+#define XC_MEM_IMPL _xc_mem_mem_t
 #include "xc_shm.h"
 #include "align.h"
 
@@ -29,7 +29,7 @@
 #define PSUB(p1, p2) (CHAR_PTR(p1) - CHAR_PTR(p2))
 
 /* {{{ mem */
-struct _xc_block_t {
+struct _xc_mem_block_t {
 #ifdef ALLOC_DEBUG_BLOCK_CHECK
 	unsigned int magic;
 #endif
@@ -37,7 +37,7 @@ struct _xc_block_t {
 	xc_block_t *next;  /* not used after alloc */
 };
 
-struct _xc_mem_t {
+struct _xc_mem_mem_t {
 	const xc_mem_handlers_t *handlers;
 	xc_shm_t                *shm;
 	xc_memsize_t size;
diff --git a/mem.h b/mem.h
index df630fb..9d35894 100644
--- a/mem.h
+++ b/mem.h
@@ -1,5 +1,18 @@
-typedef struct _xc_mem_t xc_mem_t;
-typedef struct _xc_block_t xc_block_t;
+typedef struct _xc_mem_handlers_t xc_mem_handlers_t;
+
+#ifndef XC_MEM_IMPL
+struct _xc_mem_t {
+	const xc_mem_handlers_t *handlers;
+	xc_shm_t                *shm;
+};
+#   define XC_MEM_IMPL _xc_mem_t
+#endif
+
+#ifndef XC_MEMBLOCK_IMPL
+#   define XC_MEMBLOCK_IMPL _xc_block_t
+#endif
+typedef struct XC_MEM_IMPL xc_mem_t;
+typedef struct XC_MEMBLOCK_IMPL xc_block_t;
 typedef unsigned int xc_memsize_t;
 
 /* shm::mem */
@@ -37,7 +50,7 @@ typedef unsigned int xc_memsize_t;
 	, xc_##name##_destroy          \
 }
 
-typedef struct {
+struct _xc_mem_handlers_t {
 	XC_MEM_MALLOC((*malloc));
 	XC_MEM_FREE((*free));
 	XC_MEM_CALLOC((*calloc));
@@ -53,14 +66,7 @@ typedef struct {
 
 	XC_MEM_INIT((*init));
 	XC_MEM_DESTROY((*destroy));
-} xc_mem_handlers_t;
-
-#ifndef XC_MEM_IMPL
-struct _xc_mem_t {
-	const xc_mem_handlers_t *handlers;
-	xc_shm_t                *shm;
 };
-#endif
 
 int xc_mem_scheme_register(const char *name, const xc_mem_handlers_t *handlers);
 const xc_mem_handlers_t *xc_mem_scheme_find(const char *name);
diff --git a/mmap.c b/mmap.c
index 33f74ff..6f96338 100644
--- a/mmap.c
+++ b/mmap.c
@@ -31,7 +31,7 @@
 #endif
 
 #include "php.h"
-#define XC_SHM_IMPL
+#define XC_SHM_IMPL _xc_mmap_shm_t
 #include "xc_shm.h"
 
 #ifndef max
@@ -39,7 +39,7 @@
 #endif
 
 /* {{{ xc_shm_t */
-struct _xc_shm_t {
+struct _xc_mmap_shm_t {
 	xc_shm_handlers_t *handlers;
 	void *ptr;
 	void *ptr_ro;
diff --git a/xc_malloc.c b/xc_malloc.c
index f79dccf..47b1112 100644
--- a/xc_malloc.c
+++ b/xc_malloc.c
@@ -1,5 +1,5 @@
-#define XC_SHM_IMPL
-#define XC_MEM_IMPL
+#define XC_SHM_IMPL _xc_malloc_shm_t
+#define XC_MEM_IMPL _xc_malloc_mem_t
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -7,7 +7,7 @@
 #include "php.h"
 #include "align.h"
 
-struct _xc_mem_t {
+struct _xc_malloc_mem_t {
 	const xc_mem_handlers_t *handlers;
 	xc_shm_t                *shm;
 	xc_memsize_t size;
@@ -105,8 +105,8 @@ static XC_MEM_DESTROY(xc_mem_malloc_destroy) /* {{{ */
 }
 /* }}} */
 
-/* {{{ xc_shm_t */
-struct _xc_shm_t {
+/* {{{ _xc_malloc_shm_t */
+struct _xc_malloc_shm_t {
 	xc_shm_handlers_t *handlers;
 	xc_shmsize_t       size;
 	xc_shmsize_t       memoffset;
diff --git a/xc_shm.h b/xc_shm.h
index 1717e48..fb36d10 100644
--- a/xc_shm.h
+++ b/xc_shm.h
@@ -1,4 +1,13 @@
-typedef struct _xc_shm_t xc_shm_t;
+typedef struct _xc_shm_handlers_t xc_shm_handlers_t;
+
+#ifndef XC_SHM_IMPL
+struct _xc_shm_t {
+	const xc_shm_handlers_t *handlers;
+};
+#define XC_SHM_IMPL _xc_shm_t
+#endif
+
+typedef struct XC_SHM_IMPL xc_shm_t;
 typedef size_t xc_shmsize_t;
 
 #include "mem.h"
@@ -31,7 +40,7 @@ typedef size_t xc_shmsize_t;
 	, xc_##name##_memdestroy       \
 }
 
-typedef struct {
+struct _xc_shm_handlers_t {
 	const xc_mem_handlers_t *memhandlers;
 	XC_SHM_CAN_READONLY((*can_readonly));
 	XC_SHM_IS_READWRITE((*is_readwrite));
@@ -43,14 +52,8 @@ typedef struct {
 
 	XC_SHM_MEMINIT((*meminit));
 	XC_SHM_MEMDESTROY((*memdestroy));
-} xc_shm_handlers_t;
-
-
-#ifndef XC_SHM_IMPL
-struct _xc_shm_t {
-	const xc_shm_handlers_t *handlers;
 };
-#endif
+
 typedef struct _xc_shm_scheme_t xc_shm_scheme_t;
 
 void xc_shm_init_modules();