diff --git a/README.md b/README.md
index 7df1af5..5ccbace 100644
--- a/README.md
+++ b/README.md
@@ -14,14 +14,26 @@ The API should still be considered experimental, but I'm not expecting changes a
 
 ## Compatibility
 
-The driver currently only builds on Unix, tested on Mac Os X and Linux so far. It's compatible with MongoDB 2.4 up to 3.4 and
-has full replica set and SSL support.
+The driver currently only builds on Unix, tested on Mac Os X and Linux so far. It's compatible with MongoDB 2.6 up to 3.4 and has full replica set and SSL support.
 
 ## Installation
 
 If you have any trouble installing the crate (linking openssl can be
 tricky) please check out the [installation instructions for the C driver](http://mongoc.org/libmongoc/current/installing.html).
 
+To build on Mac install OpenSSL 1.1:
+
+```
+brew install openssl@1.1
+```
+
+Export these env vars the before you make a clean build:
+
+```
+export LDFLAGS="-L/usr/local/opt/openssl@1.1/lib"
+export CPPFLAGS="-I/usr/local/opt/openssl@1.1/include"
+``
+
 ## Logging
 
 All internal logging by mongoc is redirected to the macros in the [log
diff --git a/mongoc-sys/src/lib.rs b/mongoc-sys/src/lib.rs
index f6bdbcb..57cf709 100644
--- a/mongoc-sys/src/lib.rs
+++ b/mongoc-sys/src/lib.rs
@@ -249,4 +249,6 @@ pub mod bindings {
     pub const MONGOC_ERROR_QUERY_COMMAND_NOT_FOUND: ::libc::c_uint = 59;
     pub const MONGOC_ERROR_QUERY_NOT_TAILABLE: ::libc::c_uint = 13051;
     pub const MONGOC_ERROR_PROTOCOL_ERROR: ::libc::c_uint = 17;
+    pub const MONGOC_ERROR_WRITE_CONCERN_ERROR: ::libc::c_uint = 64;
+    pub const MONGOC_ERROR_DUPLICATE_KEY: ::libc::c_uint = 11000;
 }
diff --git a/src/error.rs b/src/error.rs
index 7128798..ad41580 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -146,7 +146,9 @@ pub enum MongoErrorCode {
     ScramProtocolError,
     QueryCommandNotFound,
     QueryNotTailable,
-    Unknown
+    WriteConcernError,
+    DuplicateKey,
+    Unknown(u32)
 }
 
 impl BsoncError {
@@ -222,7 +224,9 @@ impl BsoncError {
             bindings::MONGOC_ERROR_SCRAM_PROTOCOL_ERROR          => MongoErrorCode::ScramProtocolError,
             bindings::MONGOC_ERROR_QUERY_COMMAND_NOT_FOUND       => MongoErrorCode::QueryCommandNotFound,
             bindings::MONGOC_ERROR_QUERY_NOT_TAILABLE            => MongoErrorCode::QueryNotTailable,
-            _                                                    => MongoErrorCode::Unknown
+            bindings::MONGOC_ERROR_WRITE_CONCERN_ERROR           => MongoErrorCode::WriteConcernError,
+            bindings::MONGOC_ERROR_DUPLICATE_KEY                 => MongoErrorCode::DuplicateKey,
+            code                                                 => MongoErrorCode::Unknown(code)
         }
     }