diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index aa51556..a713313 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -665,8 +665,8 @@
  *
  * \return         0 if successful,
  *                 MBEDTLS_ERR_MPI_ALLOC_FAILED if memory allocation failed,
- *                 MBEDTLS_ERR_MPI_BAD_INPUT_DATA if N is negative or nil
-                   MBEDTLS_ERR_MPI_NOT_ACCEPTABLE if A has no inverse mod N
+ *                 MBEDTLS_ERR_MPI_BAD_INPUT_DATA if N is <= 1,
+                   MBEDTLS_ERR_MPI_NOT_ACCEPTABLE if A has no inverse mod N.
  */
 int mbedtls_mpi_inv_mod( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi *N );
 
diff --git a/library/bignum.c b/library/bignum.c
index efc1a51..8df2510 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1893,7 +1893,7 @@
     int ret;
     mbedtls_mpi G, TA, TU, U1, U2, TB, TV, V1, V2;
 
-    if( mbedtls_mpi_cmp_int( N, 0 ) <= 0 )
+    if( mbedtls_mpi_cmp_int( N, 1 ) <= 0 )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
     mbedtls_mpi_init( &TA ); mbedtls_mpi_init( &TU ); mbedtls_mpi_init( &U1 ); mbedtls_mpi_init( &U2 );
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 84cdc1f..17cf350 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -550,6 +550,9 @@
 Base test mbedtls_mpi_inv_mod #4
 mbedtls_mpi_inv_mod:10:"2":10:"4":10:"0":MBEDTLS_ERR_MPI_NOT_ACCEPTABLE
 
+Base test mbedtls_mpi_inv_mod #5
+mbedtls_mpi_inv_mod:10:"3":10:"1":10:"0":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+
 Test mbedtls_mpi_inv_mod #1
 mbedtls_mpi_inv_mod:16:"aa4df5cb14b4c31237f98bd1faf527c283c2d0f3eec89718664ba33f9762907c":16:"fffbbd660b94412ae61ead9c2906a344116e316a256fd387874c6c675b1d587d":16:"8d6a5c1d7adeae3e94b9bcd2c47e0d46e778bc8804a2cc25c02d775dc3d05b0c":0