diff --git a/library/bignum.c b/library/bignum.c
index 0e587f1..7841bea 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -883,7 +883,7 @@
 {
     int ret;
     size_t i, j;
-    mbedtls_mpi_uint *o, *p, c;
+    mbedtls_mpi_uint *o, *p, c, tmp;
 
     if( X == B )
     {
@@ -906,10 +906,14 @@
 
     o = B->p; p = X->p; c = 0;
 
+    /*
+     * tmp is used because it might happen that p == o
+     */
     for( i = 0; i < j; i++, o++, p++ )
     {
+        tmp= *o;
         *p +=  c; c  = ( *p <  c );
-        *p += *o; c += ( *p < *o );
+        *p += tmp; c += ( *p < tmp );
     }
 
     while( c != 0 )
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index f838f3b..3fd7f2d 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -295,6 +295,15 @@
 Test mbedtls_mpi_add_mpi #2
 mbedtls_mpi_add_mpi:10:"643808006803554439230129854961492699151386107534013432918073439524138264842370630061369715394739134090922937332590384720397133335969549256322620979036686633213903952966175107096769180017646161851573147596390153":10:"56125680981752282333498088313568935051383833838594899821664631784577337171193624243181360054669678410455329112434552942717084003541384594864129940145043086760031292483340068923506115878221189886491132772739661669044958531131327771":10:"56125680981752282334141896320372489490613963693556392520816017892111350604111697682705498319512049040516698827829292076808006940873974979584527073481012636016353913462376755556720019831187364993587901952757307830896531678727717924"
 
+Base test mbedtls_mpi_add_mpi inplace #1
+mbedtls_mpi_add_mpi_inplace:10:"12345678":10:"24691356"
+
+Test mbedtls_mpi_add_mpi inplace #2 
+mbedtls_mpi_add_mpi_inplace:10:"643808006803554439230129854961492699151386107534013432918073439524138264842370630061369715394739134090922937332590384720397133335969549256322620979036686633213903952966175107096769180017646161851573147596390153":10:"1287616013607108878460259709922985398302772215068026865836146879048276529684741260122739430789478268181845874665180769440794266671939098512645241958073373266427807905932350214193538360035292323703146295192780306"
+
+Test mbedtls_mpi_add_mpi inplace #3 
+mbedtls_mpi_add_mpi_inplace:16:"ffffffffffffffffffffffffffffffff":16:"01fffffffffffffffffffffffffffffffe"
+
 Test mbedtls_mpi_add_int #1
 mbedtls_mpi_add_int:10:"2039568783564019774057658669290345772801939933143482630947726464532830627227012776329":9871232:10:"2039568783564019774057658669290345772801939933143482630947726464532830627227022647561"
 
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 5dd6f0d..c41ca69 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -443,6 +443,32 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
+void mbedtls_mpi_add_mpi_inplace( int radix_X, char *input_X, int radix_A, char *input_A )
+{
+    mbedtls_mpi X, A;
+    mbedtls_mpi_init( &X ); mbedtls_mpi_init( &A );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &A, radix_A, input_A ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_sub_abs( &X, &X, &X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_cmp_int( &X, 0 ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_add_abs( &X, &X, &X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &X, &A ) == 0 );
+
+    TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_add_mpi( &X, &X, &X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &X, &A ) == 0 );
+
+exit:
+    mbedtls_mpi_free( &X ); mbedtls_mpi_free( &A );
+}
+/* END_CASE */
+
+
+/* BEGIN_CASE */
 void mbedtls_mpi_add_abs( int radix_X, char *input_X, int radix_Y, char *input_Y,
                   int radix_A, char *input_A )
 {