diff --git a/wolfcrypt/src/ecc.c b/wolfcrypt/src/ecc.c
index 76c3c2f45..42bce2166 100644
--- a/wolfcrypt/src/ecc.c
+++ b/wolfcrypt/src/ecc.c
@@ -6934,6 +6934,17 @@ int wc_ecc_import_point_der_ex(byte* in, word32 inLen, const int curve_idx,
                     (ECC_CURVE_FIELD_PRIME | ECC_CURVE_FIELD_AF |
                         ECC_CURVE_FIELD_BF));
 
+        #if defined(WOLFSSL_CUSTOM_CURVES) && \
+            defined(WOLFSSL_VALIDATE_ECC_IMPORT)
+            /* validate prime is prime for custom curves */
+            if (err == MP_OKAY && curve_idx == ECC_CUSTOM_IDX) {
+                int isPrime = MP_NO;
+                err = mp_prime_is_prime(curve->prime, 8, &isPrime);
+                if (err == MP_OKAY && isPrime == MP_NO)
+                    err = MP_VAL;
+            }
+        #endif
+
             /* compute x^3 */
             if (err == MP_OKAY)
                 err = mp_sqr(point->x, &t1);
@@ -7831,6 +7842,17 @@ int wc_ecc_import_x963_ex(const byte* in, word32 inLen, ecc_key* key,
                 (ECC_CURVE_FIELD_PRIME | ECC_CURVE_FIELD_AF |
                  ECC_CURVE_FIELD_BF));
 
+    #if defined(WOLFSSL_CUSTOM_CURVES) && \
+        defined(WOLFSSL_VALIDATE_ECC_IMPORT)
+        /* validate prime is prime for custom curves */
+        if (err == MP_OKAY && key->idx == ECC_CUSTOM_IDX) {
+            int isPrime = MP_NO;
+            err = mp_prime_is_prime(curve->prime, 8, &isPrime);
+            if (err == MP_OKAY && isPrime == MP_NO)
+                err = MP_VAL;
+        }
+    #endif
+
         /* compute x^3 */
         if (err == MP_OKAY)
             err = mp_sqr(key->pubkey.x, &t1);