diff --git a/doc/dox_comments/header_files/signature.h b/doc/dox_comments/header_files/signature.h
index 6113887837..cf30d61e3e 100644
--- a/doc/dox_comments/header_files/signature.h
+++ b/doc/dox_comments/header_files/signature.h
@@ -4,13 +4,22 @@
     \brief This function returns the maximum size of the resulting signature.
 
     \return Returns SIG_TYPE_E if sig_type is not supported. Returns
-    BAD_FUNC_ARG if sig_type was invalid. A positive return value indicates
+    BAD_FUNC_ARG if sig_type was invalid or key_len does not exactly match
+    the size of the expected key structure. A positive return value indicates
     the maximum size of a signature.
 
     \param sig_type A signature type enum value such as
     WC_SIGNATURE_TYPE_ECC or WC_SIGNATURE_TYPE_RSA.
-    \param key Pointer to a key structure such as ecc_key or RsaKey.
-    \param key_len Size of the key structure.
+    \param key Pointer to the key structure corresponding to sig_type:
+    pass an ecc_key* (cast to const void*) for
+    WC_SIGNATURE_TYPE_ECC, or a RsaKey* for
+    WC_SIGNATURE_TYPE_RSA / WC_SIGNATURE_TYPE_RSA_W_ENC.
+    The caller is responsible for ensuring the pointer refers to the correct
+    type; this function cannot verify the actual runtime type of the object.
+    \param key_len Must be exactly sizeof(ecc_key) or
+    sizeof(RsaKey) matching the sig_type. Passing any other value
+    causes the function to return BAD_FUNC_ARG without dereferencing key.
+    The conventional idiom is to pass sizeof(*key) at the call site.
 
     _Example_
     \code
@@ -43,16 +52,19 @@ int wc_SignatureGetSize(enum wc_SignatureType sig_type,
     \return BAD_FUNC_ARG -173, bad function argument provided
     \return BUFFER_E -132, output buffer too small or input too large.
 
-    \param hash_type A hash type from the “enum  wc_HashType” such as
-    “WC_HASH_TYPE_SHA256”.
+    \param hash_type A hash type from the "enum  wc_HashType" such as
+    "WC_HASH_TYPE_SHA256".
     \param sig_type A signature type enum value such as
     WC_SIGNATURE_TYPE_ECC or WC_SIGNATURE_TYPE_RSA.
     \param data Pointer to buffer containing the data to hash.
     \param data_len Length of the data buffer.
     \param sig Pointer to buffer to output signature.
     \param sig_len Length of the signature output buffer.
-    \param key Pointer to a key structure such as ecc_key or RsaKey.
-    \param key_len Size of the key structure.
+    \param key Pointer to the key structure corresponding to sig_type.
+    See wc_SignatureGetSize() for the type-safety constraints that apply
+    to this parameter.
+    \param key_len Must be exactly sizeof(ecc_key) or
+    sizeof(RsaKey) matching sig_type. See wc_SignatureGetSize().
 
     _Example_
     \code
@@ -93,16 +105,19 @@ int wc_SignatureVerify(
     \return BAD_FUNC_ARG -173, bad function argument provided
     \return BUFFER_E -132, output buffer too small or input too large.
 
-    \param hash_type A hash type from the “enum  wc_HashType”
-    such as “WC_HASH_TYPE_SHA256”.
+    \param hash_type A hash type from the "enum  wc_HashType"
+    such as "WC_HASH_TYPE_SHA256".
     \param sig_type A signature type enum value such as
     WC_SIGNATURE_TYPE_ECC or WC_SIGNATURE_TYPE_RSA.
     \param data Pointer to buffer containing the data to hash.
     \param data_len Length of the data buffer.
     \param sig Pointer to buffer to output signature.
     \param sig_len Length of the signature output buffer.
-    \param key Pointer to a key structure such as ecc_key or RsaKey.
-    \param key_len Size of the key structure.
+    \param key Pointer to the key structure corresponding to sig_type.
+    See wc_SignatureGetSize() for the type-safety constraints that apply
+    to this parameter.
+    \param key_len Must be exactly sizeof(ecc_key) or
+    sizeof(RsaKey) matching sig_type. See wc_SignatureGetSize().
     \param rng Pointer to an initialized RNG structure.
 
     _Example_
@@ -166,8 +181,11 @@ int wc_SignatureGenerate(
     \param hash_len Length of the hash buffer
     \param sig Pointer to buffer containing the signature
     \param sig_len Length of the signature buffer
-    \param key Pointer to a key structure such as ecc_key or RsaKey
-    \param key_len Size of the key structure
+    \param key Pointer to the key structure corresponding to sig_type.
+    See wc_SignatureGetSize() for the type-safety constraints that apply
+    to this parameter.
+    \param key_len Must be exactly sizeof(ecc_key) or
+    sizeof(RsaKey) matching sig_type. See wc_SignatureGetSize().
 
     _Example_
     \code
@@ -216,8 +234,11 @@ int wc_SignatureVerifyHash(enum wc_HashType hash_type,
     \param hash_len Length of the hash buffer
     \param sig Pointer to buffer to output signature
     \param sig_len Pointer to length of signature output buffer
-    \param key Pointer to a key structure such as ecc_key or RsaKey
-    \param key_len Size of the key structure
+    \param key Pointer to the key structure corresponding to sig_type.
+    See wc_SignatureGetSize() for the type-safety constraints that apply
+    to this parameter.
+    \param key_len Must be exactly sizeof(ecc_key) or
+    sizeof(RsaKey) matching sig_type. See wc_SignatureGetSize().
     \param rng Pointer to an initialized RNG structure
 
     _Example_
@@ -266,8 +287,11 @@ int wc_SignatureGenerateHash(enum wc_HashType hash_type,
     \param hash_len Length of the hash buffer
     \param sig Pointer to buffer to output signature
     \param sig_len Pointer to length of signature output buffer
-    \param key Pointer to a key structure such as ecc_key or RsaKey
-    \param key_len Size of the key structure
+    \param key Pointer to the key structure corresponding to sig_type.
+    See wc_SignatureGetSize() for the type-safety constraints that apply
+    to this parameter.
+    \param key_len Must be exactly sizeof(ecc_key) or
+    sizeof(RsaKey) matching sig_type. See wc_SignatureGetSize().
     \param rng Pointer to an initialized RNG structure
     \param verify If non-zero, verify the signature after generation
 
@@ -317,8 +341,11 @@ int wc_SignatureGenerateHash_ex(enum wc_HashType hash_type,
     \param data_len Length of the data buffer
     \param sig Pointer to buffer to output signature
     \param sig_len Pointer to length of signature output buffer
-    \param key Pointer to a key structure such as ecc_key or RsaKey
-    \param key_len Size of the key structure
+    \param key Pointer to the key structure corresponding to sig_type.
+    See wc_SignatureGetSize() for the type-safety constraints that apply
+    to this parameter.
+    \param key_len Must be exactly sizeof(ecc_key) or
+    sizeof(RsaKey) matching sig_type. See wc_SignatureGetSize().
     \param rng Pointer to an initialized RNG structure
     \param verify If non-zero, verify the signature after generation
 
diff --git a/tests/api/test_signature.c b/tests/api/test_signature.c
index 88f89e54d7..63eb7ae29e 100644
--- a/tests/api/test_signature.c
+++ b/tests/api/test_signature.c
@@ -68,6 +68,13 @@ int test_wc_SignatureGetSize_ecc(void)
     sig_type = WC_SIGNATURE_TYPE_ECC;
     ExpectIntEQ(wc_SignatureGetSize(sig_type, NULL, key_len), 0);
     key_len = (word32)0;
+    ExpectIntEQ(wc_SignatureGetSize(sig_type, &ecc, key_len),
+        WC_NO_ERR_TRACE(BAD_FUNC_ARG));
+    /* key_len must be exactly sizeof(ecc_key): one less or one more is invalid */
+    key_len = (word32)(sizeof(ecc_key) - 1);
+    ExpectIntEQ(wc_SignatureGetSize(sig_type, &ecc, key_len),
+        WC_NO_ERR_TRACE(BAD_FUNC_ARG));
+    key_len = (word32)(sizeof(ecc_key) + 1);
     ExpectIntEQ(wc_SignatureGetSize(sig_type, &ecc, key_len),
         WC_NO_ERR_TRACE(BAD_FUNC_ARG));
 
@@ -138,6 +145,13 @@ int test_wc_SignatureGetSize_rsa(void)
     ExpectIntEQ(wc_SignatureGetSize(sig_type, NULL, key_len),
         WC_NO_ERR_TRACE(BAD_FUNC_ARG));
     key_len = (word32)0;
+    ExpectIntEQ(wc_SignatureGetSize(sig_type, &rsa_key, key_len),
+        WC_NO_ERR_TRACE(BAD_FUNC_ARG));
+    /* key_len must be exactly sizeof(RsaKey): one less or one more is invalid */
+    key_len = (word32)(sizeof(RsaKey) - 1);
+    ExpectIntEQ(wc_SignatureGetSize(sig_type, &rsa_key, key_len),
+        WC_NO_ERR_TRACE(BAD_FUNC_ARG));
+    key_len = (word32)(sizeof(RsaKey) + 1);
     ExpectIntEQ(wc_SignatureGetSize(sig_type, &rsa_key, key_len),
         WC_NO_ERR_TRACE(BAD_FUNC_ARG));
 
diff --git a/tests/api/test_signature.h b/tests/api/test_signature.h
index cf61e12cbc..85f43c5180 100644
--- a/tests/api/test_signature.h
+++ b/tests/api/test_signature.h
@@ -29,6 +29,6 @@ int test_wc_SignatureGetSize_rsa(void);
 
 #define TEST_SIGNATURE_DECLS                                    \
     TEST_DECL_GROUP("signature", test_wc_SignatureGetSize_ecc), \
-    TEST_DECL_GROUP("signature", test_wc_SignatureGetSize_ecc)
+    TEST_DECL_GROUP("signature", test_wc_SignatureGetSize_rsa)
 
 #endif /* WOLFCRYPT_TEST_SIGNATURE_H */
diff --git a/wolfcrypt/src/signature.c b/wolfcrypt/src/signature.c
index c5d4cf0d68..aca522a215 100644
--- a/wolfcrypt/src/signature.c
+++ b/wolfcrypt/src/signature.c
@@ -93,8 +93,11 @@ int wc_SignatureGetSize(enum wc_SignatureType sig_type,
     switch(sig_type) {
         case WC_SIGNATURE_TYPE_ECC:
 #ifdef HAVE_ECC
-            /* Sanity check that void* key is at least ecc_key in size */
-            if (key_len >= sizeof(ecc_key)) {
+            /* Verify that key_len matches exactly sizeof(ecc_key).
+             * This is a necessary but not sufficient type check: the void*
+             * API cannot verify the actual runtime type of the pointed-to
+             * object.  Callers must pass a valid ecc_key* cast to void*. */
+            if (key_len == sizeof(ecc_key)) {
                 sig_len = wc_ecc_sig_size((ecc_key*)key);
             }
             else {
@@ -108,8 +111,10 @@ int wc_SignatureGetSize(enum wc_SignatureType sig_type,
         case WC_SIGNATURE_TYPE_RSA_W_ENC:
         case WC_SIGNATURE_TYPE_RSA:
 #ifndef NO_RSA
-            /* Sanity check that void* key is at least RsaKey in size */
-            if (key_len >= sizeof(RsaKey)) {
+            /* Verify that key_len matches exactly sizeof(RsaKey).
+             * Same caveat as the ECC case above: size equality is necessary
+             * but not sufficient; the caller must pass a valid RsaKey*. */
+            if (key_len == sizeof(RsaKey)) {
                 sig_len = wc_RsaEncryptSize((RsaKey*)key);
             }
             else {