diff --git a/gdtoa/gdtoaimp.h b/gdtoa/gdtoaimp.h
index ac4b59e57..69ae8765f 100644
--- a/gdtoa/gdtoaimp.h
+++ b/gdtoa/gdtoaimp.h
@@ -481,7 +481,7 @@ extern double rnd_prod(double, double), rnd_quot(double, double);
 #define FREE_DTOA_LOCK(n)	/*nothing*/
 #endif
 
-#define Kmax 15
+#define Kmax (sizeof(size_t) << 3)
 
  struct
 Bigint {