diff --git a/cryptography/bindings/openssl/api.py b/cryptography/bindings/openssl/api.py
index 20a85ca..ec6b923 100644
--- a/cryptography/bindings/openssl/api.py
+++ b/cryptography/bindings/openssl/api.py
@@ -14,6 +14,17 @@
 import cffi
 
 
+class OpenSSLError(Exception):
+    def __init__(self, api):
+        e = api._lib.ERR_get_error()
+        if e == 0:
+            raise SystemError("Tried to create an OpenSSLError when there was "
+                "None")
+        msg = api._ffi.new("char[]", 120)
+        api._lib.ERR_error_string(e, msg)
+        super(OpenSSLError, self).__init__(api._ffi.string(msg))
+
+
 class API(object):
     """
     OpenSSL API wrapper.
@@ -43,6 +54,8 @@
                               unsigned char *, int);
         int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *, unsigned char *, int *);
         int EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *);
+
+        unsigned long ERR_get_error();
         """)
 
     def create_block_cipher_context(self, cipher, mode):
@@ -51,13 +64,11 @@
         ciphername = b"AES-{}-CBC".format(len(cipher.key) * 8)
         evp_cipher = self._lib.EVP_get_cipherbyname(ciphername)
         if evp_cipher == self._ffi.NULL:
-            # TODO: figure out openssl errors
-            raise Exception
+            raise OpenSSLError(self)
         # TODO: only use the key and initialization_vector as needed
         res = self._lib.EVP_EncryptInit_ex(ctx, evp_cipher, self._ffi.NULL, cipher.key, mode.initialization_vector)
         if res == 0:
-            # TODO: figure out openssl errors
-            raise Exception
+            raise OpenSSLError(self)
         # TODO: this should depend on mode.padding
         self._lib.EVP_CIPHER_CTX_set_padding(ctx, 0)
         return ctx
@@ -67,8 +78,7 @@
         outlen = self._ffi.new("int *")
         res = self._lib.EVP_EncryptUpdate(ctx, buf, outlen, plaintext, len(plaintext))
         if res == 0:
-            # TODO: figure out openssl errors
-            raise Exception
+            raise OpenSSLError(self)
         return self._ffi.buffer(buf)[:outlen[0]]
 
     def finalize_encrypt_context(self, ctx):
@@ -77,13 +87,11 @@
         outlen = self._ffi.new("int *")
         res = self._lib.EVP_EncryptFinal_ex(ctx, buf, outlen)
         if res == 0:
-            # TODO: figure out openssl errors
-            raise Exception
+            raise OpenSSLError(self)
         # TODO: this should also be called if the cipher isn't finalized.
         res = self._lib.EVP_CIPHER_CTX_cleanup(ctx)
         if res == 0:
-            # TODO: figure out openssl errors
-            raise Exception
+            raise OpenSSLError(self)
         return self._ffi.buffer(buf)[:outlen[0]]