diff --git a/library/bignum.c b/library/bignum.c
index 7484900667..208d508738 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -512,6 +512,12 @@ int mbedtls_mpi_read_string( mbedtls_mpi *X, int radix, const char *s )
 
     mbedtls_mpi_init( &T );
 
+    if( s[0] == 0 )
+    {
+        mbedtls_mpi_free( X );
+        return( 0 );
+    }
+
     if( s[0] == '-' )
     {
         ++s;
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index da227ad872..2460d3fa36 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -68,13 +68,13 @@ Test mpi_read_write_string #7
 mpi_read_write_string:10:"56125680981752282334141896320372489490613963693556392520816017892111350604111697682705498319512049040516698827829292076808006940873974979584527073481012636016353913462376755556720019831187364993587901952757307830896531678727717924":16:"0941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":200:0:0
 
 Test mpi_read_write_string #8 (Empty MPI hex -> hex)
-mpi_read_write_string:16:"":16:"00":4:0:0
+mpi_read_write_string:16:"":16:"":4:0:0
 
 Test mpi_read_write_string #9 (Empty MPI hex -> dec)
 mpi_read_write_string:16:"":10:"0":4:0:0
 
 Test mpi_read_write_string #8 (Empty MPI dec -> hex)
-mpi_read_write_string:10:"":16:"00":4:0:0
+mpi_read_write_string:10:"":16:"":4:0:0
 
 Test mpi_read_write_string #9 (Empty MPI dec -> dec)
 mpi_read_write_string:10:"":10:"0":4:0:0