diff --git a/rust/bssl-sys/src/lib.rs b/rust/bssl-sys/src/lib.rs
index 718509e..9edbd08 100644
--- a/rust/bssl-sys/src/lib.rs
+++ b/rust/bssl-sys/src/lib.rs
@@ -2,8 +2,43 @@
 #![allow(non_camel_case_types)]
 #![allow(non_snake_case)]
 
-// Set in build.rs
-include!(env!("BINDGEN_RS_FILE"));
+use core::ffi::c_ulong;
+
+// Wrap the bindgen output in a module and re-export it, so we can override it
+// as needed.
+mod bindgen {
+    include!(env!("BINDGEN_RS_FILE"));
+}
+pub use bindgen::*;
+
+// bindgen does not handle C constants correctly. See
+// https://github.com/rust-lang/rust-bindgen/issues/923. Work around this bug by
+// redefining some constants with the correct type. Once the bindgen bug has
+// been fixed, remove this.
+pub const ASN1_STRFLGS_ESC_2253: c_ulong = bindgen::ASN1_STRFLGS_ESC_2253 as c_ulong;
+pub const ASN1_STRFLGS_ESC_CTRL: c_ulong = bindgen::ASN1_STRFLGS_ESC_CTRL as c_ulong;
+pub const ASN1_STRFLGS_ESC_MSB: c_ulong = bindgen::ASN1_STRFLGS_ESC_MSB as c_ulong;
+pub const ASN1_STRFLGS_ESC_QUOTE: c_ulong = bindgen::ASN1_STRFLGS_ESC_QUOTE as c_ulong;
+pub const ASN1_STRFLGS_UTF8_CONVERT: c_ulong = bindgen::ASN1_STRFLGS_UTF8_CONVERT as c_ulong;
+pub const ASN1_STRFLGS_IGNORE_TYPE: c_ulong = bindgen::ASN1_STRFLGS_IGNORE_TYPE as c_ulong;
+pub const ASN1_STRFLGS_SHOW_TYPE: c_ulong = bindgen::ASN1_STRFLGS_SHOW_TYPE as c_ulong;
+pub const ASN1_STRFLGS_DUMP_ALL: c_ulong = bindgen::ASN1_STRFLGS_DUMP_ALL as c_ulong;
+pub const ASN1_STRFLGS_DUMP_UNKNOWN: c_ulong = bindgen::ASN1_STRFLGS_DUMP_UNKNOWN as c_ulong;
+pub const ASN1_STRFLGS_DUMP_DER: c_ulong = bindgen::ASN1_STRFLGS_DUMP_DER as c_ulong;
+pub const ASN1_STRFLGS_RFC2253: c_ulong = bindgen::ASN1_STRFLGS_RFC2253 as c_ulong;
+pub const XN_FLAG_COMPAT: c_ulong = bindgen::XN_FLAG_COMPAT as c_ulong;
+pub const XN_FLAG_SEP_MASK: c_ulong = bindgen::XN_FLAG_SEP_MASK as c_ulong;
+pub const XN_FLAG_SEP_COMMA_PLUS: c_ulong = bindgen::XN_FLAG_SEP_COMMA_PLUS as c_ulong;
+pub const XN_FLAG_SEP_CPLUS_SPC: c_ulong = bindgen::XN_FLAG_SEP_CPLUS_SPC as c_ulong;
+pub const XN_FLAG_SEP_SPLUS_SPC: c_ulong = bindgen::XN_FLAG_SEP_SPLUS_SPC as c_ulong;
+pub const XN_FLAG_SEP_MULTILINE: c_ulong = bindgen::XN_FLAG_SEP_MULTILINE as c_ulong;
+pub const XN_FLAG_DN_REV: c_ulong = bindgen::XN_FLAG_DN_REV as c_ulong;
+pub const XN_FLAG_FN_MASK: c_ulong = bindgen::XN_FLAG_FN_MASK as c_ulong;
+pub const XN_FLAG_FN_SN: c_ulong = bindgen::XN_FLAG_FN_SN as c_ulong;
+pub const XN_FLAG_SPC_EQ: c_ulong = bindgen::XN_FLAG_SPC_EQ as c_ulong;
+pub const XN_FLAG_DUMP_UNKNOWN_FIELDS: c_ulong = bindgen::XN_FLAG_DUMP_UNKNOWN_FIELDS as c_ulong;
+pub const XN_FLAG_RFC2253: c_ulong = bindgen::XN_FLAG_RFC2253 as c_ulong;
+pub const XN_FLAG_ONELINE: c_ulong = bindgen::XN_FLAG_ONELINE as c_ulong;
 
 // TODO(crbug.com/boringssl/596): Remove these wrappers.
 #[cfg(unsupported_inline_wrappers)]