diff --git a/library/bignum_core.c b/library/bignum_core.c
index e020da100e..3490f7d885 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -18,6 +18,7 @@
 #include "mbedtls/platform.h"
 
 #include "bignum_core.h"
+#include "bignum_core_invasive.h"
 #include "bn_mul.h"
 #include "constant_time_internal.h"
 
@@ -1037,9 +1038,10 @@ static void mpi_core_sub_mod(mbedtls_mpi_uint *X,
  * Divide X by 2 mod N in place, assuming N is odd.
  * The input must be in [0, N) and so will the output.
  */
-static void mpi_core_div2_mod_odd(mbedtls_mpi_uint *X,
-                                  const mbedtls_mpi_uint *N,
-                                  size_t limbs)
+MBEDTLS_STATIC_TESTABLE
+void mbedtls_mpi_core_div2_mod_odd(mbedtls_mpi_uint *X,
+                                   const mbedtls_mpi_uint *N,
+                                   size_t limbs)
 {
     /* If X is odd, add N to make it even before shifting. */
     unsigned odd = (unsigned) X[0] & 1;
@@ -1200,7 +1202,7 @@ void mbedtls_mpi_core_gcd_modinv_odd(mbedtls_mpi_uint *G,
             mbedtls_mpi_core_cond_assign(t2, q, N_limbs, u_odd_v_even);
             mbedtls_mpi_core_cond_assign(t2, d, N_limbs, u_odd_v_odd);
 
-            mpi_core_div2_mod_odd(t2, N, N_limbs);
+            mbedtls_mpi_core_div2_mod_odd(t2, N, N_limbs);
 
             /* Update and possibly swap */
             memcpy(r, t1, N_limbs * ciL);
diff --git a/library/bignum_core_invasive.h b/library/bignum_core_invasive.h
index 167099dc91..a9d447f792 100644
--- a/library/bignum_core_invasive.h
+++ b/library/bignum_core_invasive.h
@@ -13,11 +13,26 @@
 
 #include "bignum_core.h"
 
-#if defined(MBEDTLS_TEST_HOOKS) && !defined(MBEDTLS_THREADING_C)
+#if defined(MBEDTLS_TEST_HOOKS)
+
+#if !defined(MBEDTLS_THREADING_C)
 
 extern void (*mbedtls_safe_codepath_hook)(void);
 extern void (*mbedtls_unsafe_codepath_hook)(void);
 
-#endif /* MBEDTLS_TEST_HOOKS && !MBEDTLS_THREADING_C */
+#endif /* !MBEDTLS_THREADING_C */
+
+/** Divide X by 2 mod N in place, assuming N is odd.
+ *
+ * \param[in,out] X     The value to divide by 2 mod \p N.
+ * \param[in]     N     The modulus. Must be odd.
+ * \param[in]     limbs The number of limbs in \p X and \p N.
+ */
+MBEDTLS_STATIC_TESTABLE
+void mbedtls_mpi_core_div2_mod_odd(mbedtls_mpi_uint *X,
+                                   const mbedtls_mpi_uint *N,
+                                   size_t limbs);
+
+#endif /* MBEDTLS_TEST_HOOKS */
 
 #endif /* MBEDTLS_BIGNUM_CORE_INVASIVE_H */
diff --git a/tests/suites/test_suite_bignum_core.function b/tests/suites/test_suite_bignum_core.function
index 61660c4851..cad9c1c0dc 100644
--- a/tests/suites/test_suite_bignum_core.function
+++ b/tests/suites/test_suite_bignum_core.function
@@ -2,6 +2,7 @@
 #include "mbedtls/bignum.h"
 #include "mbedtls/entropy.h"
 #include "bignum_core.h"
+#include "bignum_core_invasive.h"
 #include "constant_time_internal.h"
 #include "test/constant_flow.h"
 #include "test/bignum_codepath_check.h"
@@ -1529,3 +1530,36 @@ exit:
     mbedtls_free(T);
 }
 /* END_CASE */
+
+/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS */
+void mpi_core_div2_mod_odd(char *input_X, char *input_N, char *input_exp_X)
+{
+    mbedtls_mpi_uint *X = NULL;
+    size_t X_limbs = 0;
+    mbedtls_mpi_uint *N = NULL;
+    size_t N_limbs = 0;
+    mbedtls_mpi_uint *exp_X = NULL;
+    size_t exp_X_limbs = 0;
+
+    /* Read test parameters into MPI structures */
+    TEST_EQUAL(0, mbedtls_test_read_mpi_core(&X, &X_limbs, input_X));
+    TEST_EQUAL(0, mbedtls_test_read_mpi_core(&N, &N_limbs, input_N));
+    TEST_EQUAL(0, mbedtls_test_read_mpi_core(&exp_X, &exp_X_limbs, input_exp_X));
+
+    /* The function under test requires this */
+    TEST_EQUAL(X_limbs, N_limbs);
+
+    TEST_CF_SECRET(X, X_limbs * sizeof(mbedtls_mpi_uint));
+    TEST_CF_SECRET(N, N_limbs * sizeof(mbedtls_mpi_uint));
+
+    mbedtls_mpi_core_div2_mod_odd(X, N, N_limbs);
+
+    TEST_CF_PUBLIC(X, X_limbs * sizeof(mbedtls_mpi_uint));
+    TEST_EQUAL(0, mpi_core_cmp(X, X_limbs, exp_X, exp_X_limbs));
+
+exit:
+    mbedtls_free(X);
+    mbedtls_free(N);
+    mbedtls_free(exp_X);
+}
+/* END_CASE */
diff --git a/tests/suites/test_suite_bignum_core.misc.data b/tests/suites/test_suite_bignum_core.misc.data
index 67164e2f90..d4cf00f893 100644
--- a/tests/suites/test_suite_bignum_core.misc.data
+++ b/tests/suites/test_suite_bignum_core.misc.data
@@ -529,3 +529,15 @@ mpi_core_gcd_modinv_odd:"e4518a1900fce698fa3":"1a84113636607520200d":"3":""
 
 GCD-modinv random 80-bit, trivial GCD -> inverse
 mpi_core_gcd_modinv_odd:"7f2405d6de7db80a7bc":"1a84113636607520200d":"1":"15f158844a59cd7a3ed2"
+
+Div2 mod odd: even value
+mpi_core_div2_mod_odd:"4":"7":"2"
+
+Div2 mod odd: odd value, no carry
+mpi_core_div2_mod_odd:"5":"7":"6"
+
+Div2 mod odd: odd value with carry
+mpi_core_div2_mod_odd:"8000000000000001":"8000000000000003":"8000000000000002"
+
+Div2 mod odd: even value with top bit set
+mpi_core_div2_mod_odd:"8000000000000002":"8000000000000003":"4000000000000001"