diff --git a/include/openssl/ecdsa.h b/include/openssl/ecdsa.h
index 08950e3..5443ef5 100644
--- a/include/openssl/ecdsa.h
+++ b/include/openssl/ecdsa.h
@@ -73,6 +73,9 @@
 // space. On successful exit, |*sig_len| is set to the actual number of bytes
 // written. The |type| argument should be zero. It returns one on success and
 // zero otherwise.
+//
+// WARNING: |digest| must be the output of some hash function on the data to be
+// signed. Passing unhashed inputs will not result in a secure signature scheme.
 OPENSSL_EXPORT int ECDSA_sign(int type, const uint8_t *digest,
                               size_t digest_len, uint8_t *sig,
                               unsigned int *sig_len, const EC_KEY *key);
@@ -81,6 +84,10 @@
 // signature by |key| of |digest|. (The |type| argument should be zero.) It
 // returns one on success or zero if the signature is invalid or an error
 // occurred.
+//
+// WARNING: |digest| must be the output of some hash function on the data to be
+// verified. Passing unhashed inputs will not result in a secure signature
+// scheme.
 OPENSSL_EXPORT int ECDSA_verify(int type, const uint8_t *digest,
                                 size_t digest_len, const uint8_t *sig,
                                 size_t sig_len, const EC_KEY *key);
@@ -124,12 +131,19 @@
 
 // ECDSA_do_sign signs |digest_len| bytes from |digest| with |key| and returns
 // the resulting signature structure, or NULL on error.
+//
+// WARNING: |digest| must be the output of some hash function on the data to be
+// signed. Passing unhashed inputs will not result in a secure signature scheme.
 OPENSSL_EXPORT ECDSA_SIG *ECDSA_do_sign(const uint8_t *digest,
                                         size_t digest_len, const EC_KEY *key);
 
 // ECDSA_do_verify verifies that |sig| constitutes a valid signature by |key|
 // of |digest|. It returns one on success or zero if the signature is invalid
 // or on error.
+//
+// WARNING: |digest| must be the output of some hash function on the data to be
+// verified. Passing unhashed inputs will not result in a secure signature
+// scheme.
 OPENSSL_EXPORT int ECDSA_do_verify(const uint8_t *digest, size_t digest_len,
                                    const ECDSA_SIG *sig, const EC_KEY *key);