diff --git a/library/base64.c b/library/base64.c
index c492cc0..2b43a94 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -61,6 +61,8 @@
      49,  50,  51, 127, 127, 127, 127, 127
 };
 
+#define BASE64_SIZE_T_MAX   ( (size_t) -1 ) /* SIZE_T_MAX is not standard */
+
 /*
  * Encode a buffer into base64 format
  */
@@ -79,9 +81,9 @@
 
     n = slen / 3 + ( slen % 3 != 0 );
 
-    if( n > ( SIZE_T_MAX - 1 ) / 4 )
+    if( n > ( BASE64_SIZE_T_MAX - 1 ) / 4 )
     {
-        *dlen = SIZE_T_MAX;
+        *dlen = BASE64_SIZE_T_MAX;
         return( POLARSSL_ERR_BASE64_BUFFER_TOO_SMALL );
     }
 
diff --git a/library/bignum.c b/library/bignum.c
index 9544dc9..14a3dc7 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -34,7 +34,6 @@
 #include "polarssl/bignum.h"
 #include "polarssl/bn_mul.h"
 
-#include <limits.h>
 #include <stdlib.h>
 
 /* Implementation that should never be optimized out by the compiler */
@@ -46,6 +45,8 @@
 #define biL    (ciL << 3)               /* bits  in limb  */
 #define biH    (ciL << 2)               /* half limb size */
 
+#define MPI_SIZE_T_MAX  ( (size_t) -1 ) /* SIZE_T_MAX is not standard */
+
 /*
  * Convert between bits/chars and number of limbs
  * Divide first in order to avoid potential overflows
@@ -289,7 +290,7 @@
 
     if( radix == 16 )
     {
-        if( slen > SIZE_T_MAX >> 2 )
+        if( slen > MPI_SIZE_T_MAX >> 2 )
             return( POLARSSL_ERR_MPI_BAD_INPUT_DATA );
 
         n = BITS_TO_LIMBS( slen << 2 );