diff --git a/scripts/mbedtls_dev/bignum_mod.py b/scripts/mbedtls_dev/bignum_mod.py
index 81ece07..5f4e362 100644
--- a/scripts/mbedtls_dev/bignum_mod.py
+++ b/scripts/mbedtls_dev/bignum_mod.py
@@ -34,6 +34,25 @@
 
 # BEGIN MERGE SLOT 3
 
+class BignumModSub(bignum_common.ModOperationCommon, BignumModTarget):
+    """Test cases for bignum mpi_mod_sub()."""
+    symbol = "-"
+    test_function = "mpi_mod_sub"
+    test_name = "mbedtls_mpi_mod_sub"
+    input_style = "fixed"
+    arity = 2
+
+    # To make negative tests easier, append 0 for success to the generated cases
+    def arguments(self) -> List[str]:
+        return [bignum_common.quote_str(n) for n in [self.arg_n,
+                                                     self.arg_a,
+                                                     self.arg_b]
+               ] + self.result() + ["0"]
+
+    def result(self) -> List[str]:
+        result = (self.int_a - self.int_b) % self.int_n
+        return [self.format_result(result)]
+
 # END MERGE SLOT 3
 
 # BEGIN MERGE SLOT 4