diff --git a/wolfcrypt/src/hmac.c b/wolfcrypt/src/hmac.c
index edc16f1a5f..8e8ad3ff3e 100644
--- a/wolfcrypt/src/hmac.c
+++ b/wolfcrypt/src/hmac.c
@@ -1590,6 +1590,10 @@ int wolfSSL_GetHmacMaxSize(void)
         const  byte* localSalt;  /* either points to user input or tmp */
         word32 hashSz;
 
+        if (out == NULL || (inKey == NULL && inKeySz > 0)) {
+            return BAD_FUNC_ARG;
+        }
+
         ret = wc_HmacSizeByType(type);
         if (ret < 0) {
             return ret;
diff --git a/wolfcrypt/src/kdf.c b/wolfcrypt/src/kdf.c
index c6be3afc99..849b6dfa52 100644
--- a/wolfcrypt/src/kdf.c
+++ b/wolfcrypt/src/kdf.c
@@ -1009,7 +1009,8 @@ int wc_SRTP_KDF(const byte* key, word32 keySz, const byte* salt, word32 saltSz,
 
     /* Validate parameters. */
     if ((key == NULL) || (keySz > AES_256_KEY_SIZE) || (salt == NULL) ||
-            (saltSz > WC_SRTP_MAX_SALT) || (kdrIdx < -1) || (kdrIdx > 24)) {
+            (saltSz > WC_SRTP_MAX_SALT) || (kdrIdx < -1) || (kdrIdx > 24) ||
+            ((kdrIdx >= 0) && (idx == NULL))) {
         ret = BAD_FUNC_ARG;
     }
 
@@ -1103,7 +1104,8 @@ int wc_SRTCP_KDF_ex(const byte* key, word32 keySz, const byte* salt, word32 salt
 
     /* Validate parameters. */
     if ((key == NULL) || (keySz > AES_256_KEY_SIZE) || (salt == NULL) ||
-            (saltSz > WC_SRTP_MAX_SALT) || (kdrIdx < -1) || (kdrIdx > 24)) {
+            (saltSz > WC_SRTP_MAX_SALT) || (kdrIdx < -1) || (kdrIdx > 24) ||
+            ((kdrIdx >= 0) && (idx == NULL))) {
         ret = BAD_FUNC_ARG;
     }
 
@@ -1194,7 +1196,7 @@ int wc_SRTP_KDF_label(const byte* key, word32 keySz, const byte* salt,
     /* Validate parameters. */
     if ((key == NULL) || (keySz > AES_256_KEY_SIZE) || (salt == NULL) ||
             (saltSz > WC_SRTP_MAX_SALT) || (kdrIdx < -1) || (kdrIdx > 24) ||
-            (outKey == NULL)) {
+            (outKey == NULL) || ((kdrIdx >= 0) && (idx == NULL))) {
         ret = BAD_FUNC_ARG;
     }
 
@@ -1267,7 +1269,7 @@ int wc_SRTCP_KDF_label(const byte* key, word32 keySz, const byte* salt,
     /* Validate parameters. */
     if ((key == NULL) || (keySz > AES_256_KEY_SIZE) || (salt == NULL) ||
             (saltSz > WC_SRTP_MAX_SALT) || (kdrIdx < -1) || (kdrIdx > 24) ||
-            (outKey == NULL)) {
+            (outKey == NULL) || ((kdrIdx >= 0) && (idx == NULL))) {
         ret = BAD_FUNC_ARG;
     }
 
diff --git a/wolfcrypt/test/test.c b/wolfcrypt/test/test.c
index d639f523a4..b869dc1960 100644
--- a/wolfcrypt/test/test.c
+++ b/wolfcrypt/test/test.c
@@ -31466,7 +31466,18 @@ WOLFSSL_TEST_SUBROUTINE wc_test_ret_t hkdf_test(void)
 #endif /* !NO_SHA256 */
 #endif /* !NO_SHA || !NO_SHA256 */
 
-    return ret;
+#ifndef NO_SHA256
+    /* wc_HKDF_Extract bad arg: NULL out */
+    ret = wc_HKDF_Extract(WC_SHA256, NULL, 0, ikm1, (word32)sizeof(ikm1), NULL);
+    if (ret != WC_NO_ERR_TRACE(BAD_FUNC_ARG))
+        return WC_TEST_RET_ENC_EC(ret);
+    /* wc_HKDF_Extract bad arg: NULL inKey with non-zero inKeySz */
+    ret = wc_HKDF_Extract(WC_SHA256, NULL, 0, NULL, 5, okm1);
+    if (ret != WC_NO_ERR_TRACE(BAD_FUNC_ARG))
+        return WC_TEST_RET_ENC_EC(ret);
+#endif /* !NO_SHA256 */
+
+    return 0;
 }
 
 #endif /* HAVE_HKDF */
@@ -33402,6 +33413,24 @@ WOLFSSL_TEST_SUBROUTINE wc_test_ret_t srtpkdf_test(void)
     if (ret != WC_NO_ERR_TRACE(BAD_FUNC_ARG))
         ERROR_OUT(WC_TEST_RET_ENC_EC(ret), out);
 
+    /* kdrIdx >= 0 requires non-NULL idx. */
+    ret = wc_SRTP_KDF(tv[i].key, tv[i].keySz, tv[i].salt, tv[i].saltSz,
+        0, NULL, keyE, tv[i].keSz, keyA, tv[i].kaSz, keyS, tv[i].ksSz);
+    if (ret != WC_NO_ERR_TRACE(BAD_FUNC_ARG))
+        ERROR_OUT(WC_TEST_RET_ENC_EC(ret), out);
+    ret = wc_SRTCP_KDF(tv[i].key, tv[i].keySz, tv[i].salt, tv[i].saltSz,
+        0, NULL, keyE, tv[i].keSz, keyA, tv[i].kaSz, keyS, tv[i].ksSz);
+    if (ret != WC_NO_ERR_TRACE(BAD_FUNC_ARG))
+        ERROR_OUT(WC_TEST_RET_ENC_EC(ret), out);
+    ret = wc_SRTP_KDF_label(tv[i].key, tv[i].keySz, tv[i].salt, tv[i].saltSz,
+        0, NULL, WC_SRTP_LABEL_ENCRYPTION, keyE, tv[i].keSz);
+    if (ret != WC_NO_ERR_TRACE(BAD_FUNC_ARG))
+        ERROR_OUT(WC_TEST_RET_ENC_EC(ret), out);
+    ret = wc_SRTCP_KDF_label(tv[i].key, tv[i].keySz, tv[i].salt, tv[i].saltSz,
+        0, NULL, WC_SRTCP_LABEL_ENCRYPTION, keyE, tv[i].keSz);
+    if (ret != WC_NO_ERR_TRACE(BAD_FUNC_ARG))
+        ERROR_OUT(WC_TEST_RET_ENC_EC(ret), out);
+
     ret = wc_SRTP_KDF(tv[i].key, tv[i].keySz, tv[i].salt, tv[i].saltSz,
         tv[i].kdfIdx, tv[i].index, NULL, tv[i].keSz, keyA, tv[i].kaSz,
         keyS, tv[i].ksSz);