diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 146224a..aa51556 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -122,6 +122,7 @@
      #define MBEDTLS_HAVE_INT64
      typedef  int64_t mbedtls_mpi_sint;
      typedef uint64_t mbedtls_mpi_uint;
+     /* mbedtls_t_udbl defined as 128-bit unsigned int */
      typedef unsigned int mbedtls_t_udbl __attribute__((mode(TI)));
      #define MBEDTLS_HAVE_UDBL
   #else
diff --git a/library/bignum.c b/library/bignum.c
index 21069d8..0e587f1 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1221,10 +1221,11 @@
 #if defined(MBEDTLS_HAVE_UDBL)
     mbedtls_t_udbl dividend, quotient;
 #else
-    const mbedtls_mpi_uint radix = 1 << biH;
+    const mbedtls_mpi_uint radix = (mbedtls_mpi_uint) 1 << biH;
+    const mbedtls_mpi_uint uint_halfword_mask = ( (mbedtls_mpi_uint) 1 << biH ) - 1;
     mbedtls_mpi_uint d0, d1, q0, q1, rAX, r0, quotient;
     mbedtls_mpi_uint u0_msw, u0_lsw;
-    int s;
+    size_t s;
 #endif
 
     /*
@@ -1245,7 +1246,7 @@
         quotient = ( (mbedtls_t_udbl) 1 << biL ) - 1;
 
     if( r != NULL )
-        *r = dividend - (quotient * d);
+        *r = (mbedtls_mpi_uint)( dividend - (quotient * d ) );
 
     return (mbedtls_mpi_uint) quotient;
 #else
@@ -1262,14 +1263,14 @@
     d = d << s;
 
     u1 = u1 << s;
-    u1 |= ( u0 >> ( 32 - s ) ) & ( -s >> 31 );
+    u1 |= ( u0 >> ( biL - s ) ) & ( -(mbedtls_mpi_sint)s >> ( biL - 1 ) );
     u0 =  u0 << s;
 
     d1 = d >> biH;
-    d0 = d & 0xffff;
+    d0 = d & uint_halfword_mask;
 
     u0_msw = u0 >> biH;
-    u0_lsw = u0 & 0xffff;
+    u0_lsw = u0 & uint_halfword_mask;
 
     /*
      * Find the first quotient and remainder