diff --git a/include/polarssl/bignum.h b/include/polarssl/bignum.h
index 2db29d5ae..dc54af8cd 100644
--- a/include/polarssl/bignum.h
+++ b/include/polarssl/bignum.h
@@ -691,6 +691,8 @@ int mpi_fill_random( mpi *X, size_t size,
  *
  * \return         0 if successful,
  *                 POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
+ *                 POLARSSL_ERR_MPI_BAD_INPUT_DATA if N is <= 1,
+ *                 POLARSSL_ERR_MPI_NOT_ACCEPTABLE if A has no inverse mod N.
  */
 int mpi_gcd( mpi *G, const mpi *A, const mpi *B );
 
diff --git a/library/bignum.c b/library/bignum.c
index 211cb2af5..9d12a86cc 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1891,7 +1891,7 @@ int mpi_inv_mod( mpi *X, const mpi *A, const mpi *N )
     int ret;
     mpi G, TA, TU, U1, U2, TB, TV, V1, V2;
 
-    if( mpi_cmp_int( N, 0 ) <= 0 )
+    if( mpi_cmp_int( N, 1 ) <= 0 )
         return( POLARSSL_ERR_MPI_BAD_INPUT_DATA );
 
     mpi_init( &TA ); mpi_init( &TU ); mpi_init( &U1 ); mpi_init( &U2 );
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index cff62b4d9..52cbd7e6a 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -550,6 +550,9 @@ mpi_inv_mod:10:"3":10:"-11":10:"4":POLARSSL_ERR_MPI_BAD_INPUT_DATA
 Base test mpi_inv_mod #4
 mpi_inv_mod:10:"2":10:"4":10:"0":POLARSSL_ERR_MPI_NOT_ACCEPTABLE
 
+Base test mbedtls_mpi_inv_mod #5
+mpi_inv_mod:10:"3":10:"1":10:"0":POLARSSL_ERR_MPI_BAD_INPUT_DATA
+
 Test mpi_inv_mod #1
 mpi_inv_mod:16:"aa4df5cb14b4c31237f98bd1faf527c283c2d0f3eec89718664ba33f9762907c":16:"fffbbd660b94412ae61ead9c2906a344116e316a256fd387874c6c675b1d587d":16:"8d6a5c1d7adeae3e94b9bcd2c47e0d46e778bc8804a2cc25c02d775dc3d05b0c":0