diff --git a/doc/dox_comments/header_files/hmac.h b/doc/dox_comments/header_files/hmac.h
index 5deade4272..713b2f2260 100644
--- a/doc/dox_comments/header_files/hmac.h
+++ b/doc/dox_comments/header_files/hmac.h
@@ -254,7 +254,8 @@ int wc_HKDF_Extract(
     \param saltSz length of the salt. Use 0 if not using a salt
     \param inKey pointer to the buffer containing the key to use for KDF
     \param inKeySz length of the input key
-    \param out pointer to the buffer in which to store the derived key
+    \param out pointer to the buffer in which to store the derived key. Must be
+    digest length per hash 'type'.  See wc_HmacSizeByType()
     \param heap  heap hint to use for memory. Can be NULL
     \param devId ID to use with crypto callbacks or async hardware. Set to INVALID_DEVID (-2) if not used
 
@@ -275,6 +276,7 @@ int wc_HKDF_Extract(
     \sa wc_HKDF_Extract
     \sa wc_HKDF_Expand
     \sa wc_HKDF_Expand_ex
+    \sa wc_HmacSizeByType
 */
 int wc_HKDF_Extract_ex(
     int type,
diff --git a/wolfcrypt/src/cryptocb.c b/wolfcrypt/src/cryptocb.c
index 197a435649..9c3692b5f3 100644
--- a/wolfcrypt/src/cryptocb.c
+++ b/wolfcrypt/src/cryptocb.c
@@ -2532,6 +2532,7 @@ int wc_CryptoCb_Hkdf(int hashType, const byte* inKey, word32 inKeySz,
     return wc_CryptoCb_TranslateErrorCode(ret);
 }
 
+/* NOTE: size of 'out' must be the digest size per hashType */
 int wc_CryptoCb_Hkdf_Extract(int hashType, const byte* salt, word32 saltSz,
                         const byte* inKey, word32 inKeySz, byte* out, int devId)
 {
diff --git a/wolfcrypt/src/hmac.c b/wolfcrypt/src/hmac.c
index 48d84c60f7..a970b46fcf 100644
--- a/wolfcrypt/src/hmac.c
+++ b/wolfcrypt/src/hmac.c
@@ -1754,8 +1754,9 @@ int wolfSSL_GetHmacMaxSize(void)
         const  byte* localSalt;  /* either points to user input or tmp */
         word32 hashSz;
 
-        if (out == NULL || (inKey == NULL && inKeySz > 0))
+        if (out == NULL || (inKey == NULL && inKeySz > 0)) {
             return BAD_FUNC_ARG;
+        }
 
 #ifdef WOLF_CRYPTO_CB
         /* Try crypto callback first */
@@ -1768,8 +1769,9 @@ int wolfSSL_GetHmacMaxSize(void)
 #endif
 
         ret = wc_HmacSizeByType(type);
-        if (ret < 0)
+        if (ret < 0) {
             return ret;
+        }
         hashSz = (word32)ret;
 
         WC_ALLOC_VAR_EX(myHmac, Hmac, 1, NULL, DYNAMIC_TYPE_HMAC,
@@ -1830,12 +1832,14 @@ int wolfSSL_GetHmacMaxSize(void)
         word32 hashSz;
         byte   n = 0x1;
 
-        if (out == NULL || (inKey == NULL && inKeySz > 0))
+        if (out == NULL || (inKey == NULL && inKeySz > 0)) {
             return BAD_FUNC_ARG;
+        }
 
         ret = wc_HmacSizeByType(type);
-        if (ret < 0)
+        if (ret < 0) {
             return ret;
+        }
         hashSz = (word32)ret;
 
         /* RFC 5869 states that the length of output keying material in
diff --git a/wolfssl/wolfcrypt/cryptocb.h b/wolfssl/wolfcrypt/cryptocb.h
index 04ec375ca7..7a24e8f743 100644
--- a/wolfssl/wolfcrypt/cryptocb.h
+++ b/wolfssl/wolfcrypt/cryptocb.h
@@ -638,20 +638,20 @@ typedef struct wc_CryptoInfo {
                 int         hashType; /* WC_SHA256, etc. */
                 const byte* inKey;    /* Input keying material */
                 word32      inKeySz;
-                const byte* salt; /* Optional salt */
+                const byte* salt;   /* Optional salt */
                 word32      saltSz;
-                const byte* info; /* Optional info */
+                const byte* info;   /* Optional info */
                 word32      infoSz;
-                byte*       out; /* Output key material */
+                byte*       out;    /* Output key material */
                 word32      outSz;
             } hkdf;
             struct {                  /* HKDF extract */
                 int         hashType; /* WC_SHA256, etc. */
-                const byte* salt; /* Optional salt */
-                word32      saltSz;
+                const byte* salt;     /* Optional salt */
+                word32      saltSz;   /* must be 0 if salt==NULL */
                 const byte* inKey;    /* Input keying material */
                 word32      inKeySz;
-                byte*       out; /* Output key material */
+                byte*       out; /* out must be size of the hashType digest */
             } hkdf_extract;
             struct {                  /* HKDF expand */
                 int         hashType; /* WC_SHA256, etc. */
@@ -905,7 +905,7 @@ WOLFSSL_LOCAL int wc_CryptoCb_Hmac(Hmac* hmac, int macType, const byte* in,
     word32 inSz, byte* digest);
 #endif /* !NO_HMAC */
 
-#ifdef HAVE_HKDF
+#if defined(HAVE_HKDF) && !defined(NO_HMAC)
 WOLFSSL_LOCAL int wc_CryptoCb_Hkdf(int hashType, const byte* inKey,
                                    word32 inKeySz, const byte* salt,
                                    word32 saltSz, const byte* info,
@@ -916,7 +916,7 @@ WOLFSSL_LOCAL int wc_CryptoCb_Hkdf_Extract(int hashType, const byte* salt,
 WOLFSSL_LOCAL int wc_CryptoCb_Hkdf_Expand(int hashType, const byte* inKey,
                     word32 inKeySz, const byte* info, word32 infoSz,
                     byte* out, word32 outSz, int devId);
-#endif
+#endif /* HAVE_HKDF && !NO_HMAC */
 
 #if defined(HAVE_CMAC_KDF)
 WOLFSSL_LOCAL int wc_CryptoCb_Kdf_TwostepCmac(const byte * salt, word32 saltSz,