diff --git a/src/bits.h b/src/bits.h
index d17567f7..6f9c0cf0 100644
--- a/src/bits.h
+++ b/src/bits.h
@@ -120,6 +120,12 @@
 /* *INDENT-ON* */
 /* clang-format on */
 
+#if UINTPTR_MAX > 0xffffFFFFul || ULONG_MAX > 0xffffFFFFul
+#define MDBX_WORDBITS 64
+#else
+#define MDBX_WORDBITS 32
+#endif /* MDBX_WORDBITS */
+
 /*----------------------------------------------------------------------------*/
 /* Basic constants and types */
 
@@ -163,7 +169,7 @@
  * size up to 2^44 bytes, in case of 4K pages. */
 typedef uint32_t pgno_t;
 #define PRIaPGNO PRIu32
-#define MAX_PAGENO ((pgno_t)UINT64_C(0xffffFFFFffff))
+#define MAX_PAGENO UINT32_C(0x7FFFffff)
 #define MIN_PAGENO NUM_METAS
 
 /* A transaction ID. */
@@ -392,11 +398,13 @@ typedef struct MDBX_page {
 #else
 #define MAX_MAPSIZE32 UINT32_C(0x7ff80000)
 #endif
-#define MAX_MAPSIZE64                                                          \
-  ((sizeof(pgno_t) > 4) ? UINT64_C(0x7fffFFFFfff80000)                         \
-                        : MAX_PAGENO * (uint64_t)MAX_PAGESIZE)
+#define MAX_MAPSIZE64 (MAX_PAGENO * (uint64_t)MAX_PAGESIZE)
 
-#define MAX_MAPSIZE ((sizeof(size_t) < 8) ? MAX_MAPSIZE32 : MAX_MAPSIZE64)
+#if MDBX_WORDBITS >= 64
+#define MAX_MAPSIZE MAX_MAPSIZE64
+#else
+#define MAX_MAPSIZE MAX_MAPSIZE32
+#endif /* MDBX_WORDBITS */
 
 /* The header for the reader table (a memory-mapped lock file). */
 typedef struct MDBX_lockinfo {