diff --git a/scripts/mbedtls_dev/bignum_common.py b/scripts/mbedtls_dev/bignum_common.py
index 3ff8b2f..0339b1a 100644
--- a/scripts/mbedtls_dev/bignum_common.py
+++ b/scripts/mbedtls_dev/bignum_common.py
@@ -99,6 +99,7 @@
     limb_sizes = [32, 64] # type: List[int]
     arities = [1, 2]
     arity = 2
+    suffix = False   # for arity = 1, symbol can be prefix (default) or suffix
 
     def __init__(self, val_a: str, val_b: str = "0", bits_in_limb: int = 32) -> None:
         self.val_a = val_a
@@ -170,7 +171,8 @@
         """
         if not self.case_description:
             if self.arity == 1:
-                self.case_description = "{} {:x}".format(
+                format_string = "{1:x} {0}" if self.suffix else "{0} {1:x}"
+                self.case_description = format_string.format(
                     self.symbol, self.int_a
                 )
             elif self.arity == 2:
diff --git a/scripts/mbedtls_dev/bignum_data.py b/scripts/mbedtls_dev/bignum_data.py
index e6ed300..9658933 100644
--- a/scripts/mbedtls_dev/bignum_data.py
+++ b/scripts/mbedtls_dev/bignum_data.py
@@ -90,8 +90,8 @@
                               "4708d9893a973000b54a23020fc5b043d6e4a51519d9c9cc"
                               "52d32377e78131c1")
 
-# Adding 192 bit and 1024 bit numbers because these are the shortest required
-# for ECC and RSA respectively.
+# Adding 192 bit and 1024 bit numbers because these are the shortest required
+# for ECC and RSA respectively.
 INPUTS_DEFAULT = [
         "0", "1", # corner cases
         "2", "3", # small primes
@@ -110,13 +110,21 @@
 # supported for now.
 MODULI_DEFAULT = [
         "53", # safe prime
-        "45", # non-prime
+        "45", # non-prime
         SAFE_PRIME_192_BIT_SEED_1,  # safe prime
         RANDOM_192_BIT_SEED_2_NO4,  # not a prime
         SAFE_PRIME_1024_BIT_SEED_3, # safe prime
         RANDOM_1024_BIT_SEED_4_NO5, # not a prime
         ]
 
+# Some functions, e.g. mbedtls_mpi_mod_raw_inv_prime(), only support prime moduli.
+ONLY_PRIME_MODULI = [
+        "53", # safe prime
+        "8ac72304057392b5",     # 9999999997777777333 (longer, not safe, prime)
+        SAFE_PRIME_192_BIT_SEED_1,  # safe prime
+        SAFE_PRIME_1024_BIT_SEED_3, # safe prime
+        ]
+
 def __gen_safe_prime(bits, seed):
     '''
     Generate a safe prime.
diff --git a/scripts/mbedtls_dev/bignum_mod_raw.py b/scripts/mbedtls_dev/bignum_mod_raw.py
index d05479a..1a23a60 100644
--- a/scripts/mbedtls_dev/bignum_mod_raw.py
+++ b/scripts/mbedtls_dev/bignum_mod_raw.py
@@ -18,6 +18,7 @@
 
 from . import test_data_generation
 from . import bignum_common
+from .bignum_data import ONLY_PRIME_MODULI
 
 class BignumModRawTarget(test_data_generation.BaseTarget):
     #pylint: disable=abstract-method, too-few-public-methods
@@ -53,6 +54,36 @@
 
 # BEGIN MERGE SLOT 3
 
+class BignumModRawInvPrime(bignum_common.ModOperationCommon,
+                           BignumModRawTarget):
+    """Test cases for bignum mpi_mod_raw_inv_prime()."""
+    moduli = ONLY_PRIME_MODULI
+    symbol = "^ -1"
+    test_function = "mpi_mod_raw_inv_prime"
+    test_name = "mbedtls_mpi_mod_raw_inv_prime (Montgomery form only)"
+    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 arguments(self) -> List[str]:
+        # Input has to be given in Montgomery form
+        mont_a = self.to_montgomery(self.int_a)
+        arg_mont_a = self.format_arg('{:x}'.format(mont_a))
+        return [bignum_common.quote_str(n) for n in [self.arg_n,
+                                                     arg_mont_a]
+               ] + self.result()
+
+    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)
+        return [self.format_result(mont_result)]
+
 # END MERGE SLOT 3
 
 # BEGIN MERGE SLOT 4