diff --git a/ChangeLog.d/fix-iar-warnings.txt b/ChangeLog.d/fix-iar-warnings.txt
new file mode 100644
index 0000000000..244e8630de
--- /dev/null
+++ b/ChangeLog.d/fix-iar-warnings.txt
@@ -0,0 +1,2 @@
+Bugfix
+   * Fix IAR compiler warnings. Contributed by Glenn Strauss in #3835.
diff --git a/library/bignum.c b/library/bignum.c
index 37193f55a8..32038f8eb1 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1559,9 +1559,9 @@ static mbedtls_mpi_uint mbedtls_int_div_int( mbedtls_mpi_uint u1,
      */
     if( 0 == d || u1 >= d )
     {
-        if (r != NULL) *r = ~0;
+        if (r != NULL) *r = ~(mbedtls_mpi_uint)0u;
 
-        return ( ~0 );
+        return ( ~(mbedtls_mpi_uint)0u );
     }
 
 #if defined(MBEDTLS_HAVE_UDBL)
@@ -1700,7 +1700,7 @@ int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A,
     for( i = n; i > t ; i-- )
     {
         if( X.p[i] >= Y.p[t] )
-            Z.p[i - t - 1] = ~0;
+            Z.p[i - t - 1] = ~(mbedtls_mpi_uint)0u;
         else
         {
             Z.p[i - t - 1] = mbedtls_int_div_int( X.p[i], X.p[i - 1],