diff --git a/scripts/mbedtls_dev/bignum_mod.py b/scripts/mbedtls_dev/bignum_mod.py
index a16699a..9f98131 100644
--- a/scripts/mbedtls_dev/bignum_mod.py
+++ b/scripts/mbedtls_dev/bignum_mod.py
@@ -18,6 +18,7 @@
 
 from . import test_data_generation
 from . import bignum_common
+from .bignum_data import ONLY_PRIME_MODULI
 
 class BignumModTarget(test_data_generation.BaseTarget):
     #pylint: disable=abstract-method, too-few-public-methods
@@ -48,6 +49,56 @@
         # generated cases
         return [self.format_result(result), "0"]
 
+class BignumModInvNonMont(bignum_common.ModOperationCommon, BignumModTarget):
+    """Test cases for bignum mpi_mod_inv() - not in Montgomery form."""
+    moduli = ONLY_PRIME_MODULI  # for now only prime moduli supported
+    symbol = "^ -1"
+    test_function = "mpi_mod_inv_non_mont"
+    test_name = "mbedtls_mpi_mod_inv non-Mont. form"
+    input_style = "fixed"
+    arity = 1
+    suffix = True
+
+    @property
+    def is_valid(self) -> bool:
+        return self.int_a > 0 and self.int_a < self.int_n
+
+    def result(self) -> List[str]:
+        result = bignum_common.invmod(self.int_a, self.int_n)
+        if result < 0:
+            result += self.int_n
+        # To make negative tests easier, append 0 for success to the
+        # generated cases
+        return [self.format_result(result), "0"]
+
+class BignumModInvMont(bignum_common.ModOperationCommon, BignumModTarget):
+    """Test cases for bignum mpi_mod_inv() - Montgomery form."""
+    moduli = ONLY_PRIME_MODULI  # for now only prime moduli supported
+    symbol = "^ -1"
+    test_function = "mpi_mod_inv_mont"
+    test_name = "mbedtls_mpi_mod_inv Mont. form"
+    input_style = "arch_split"  # Mont. form requires arch_split
+    arity = 1
+    suffix = True
+
+    @property
+    def is_valid(self) -> bool:
+        return self.int_a > 0 and self.int_a < self.int_n
+
+    @property
+    def arg_a(self) -> str:
+        mont_a = self.to_montgomery(self.int_a)
+        return self.format_arg('{:x}'.format(mont_a))
+
+    def result(self) -> List[str]:
+        result = bignum_common.invmod(self.int_a, self.int_n)
+        if result < 0:
+            result += self.int_n
+        mont_result = self.to_montgomery(result)
+        # To make negative tests easier, append 0 for success to the
+        # generated cases
+        return [self.format_result(mont_result), "0"]
+
 # END MERGE SLOT 3
 
 # BEGIN MERGE SLOT 4