diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 3fd7f2d..0d4ee44 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -46,6 +46,9 @@
 Test mpi_read_write_string #9 (Empty MPI -> dec)
 mpi_read_write_string:16:"":10:"0":4:0:0
 
+Test mpi_write_string #10 (Negative hex with odd number of digits)
+mpi_read_write_string:16:"-1":16:"":3:0:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
 Base test mbedtls_mpi_read_binary #1
 mbedtls_mpi_read_binary:"0941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":10:"56125680981752282334141896320372489490613963693556392520816017892111350604111697682705498319512049040516698827829292076808006940873974979584527073481012636016353913462376755556720019831187364993587901952757307830896531678727717924"