diff --git a/Cargo.toml b/Cargo.toml
index 4c61dd7e770f49547574e442a3dafc71eec3a900..4af5bac9e1c6f4b9753b0dcac95ec96d40c550a6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,6 +3,7 @@
 name = "openssl"
 version = "0.0.0"
 authors = ["Steven Fackler <sfackler@gmail.com"]
+build = "make"
 
 [lib]
 
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..c88ebeaec1fa6a641b278c739513c95128caf0df
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,4 @@
+default:
+	rm -f $(OUT_DIR)/bin_is_zero.o
+	$(CC) -O -shared native/bn_is_zero.c -o bn_is_zero.o
+	mv bn_is_zero.o $(OUT_DIR)
diff --git a/native/bn_is_zero.c b/native/bn_is_zero.c
new file mode 100644
index 0000000000000000000000000000000000000000..b0a4300b47068ce69eefaf544599ac9610c50e93
--- /dev/null
+++ b/native/bn_is_zero.c
@@ -0,0 +1,4 @@
+#include <openssl/bn.h>
+
+int bn_is_zero(BIGNUM *x) { return BN_is_zero(x); }
+
diff --git a/native/bn_is_zero.h b/native/bn_is_zero.h
new file mode 100644
index 0000000000000000000000000000000000000000..8ec36c35d4aceec910c78654881f657e67592a0e
--- /dev/null
+++ b/native/bn_is_zero.h
@@ -0,0 +1 @@
+int bn_is_zero(BIGNUM *x);
diff --git a/src/ffi.rs b/src/ffi.rs
index b31dc1bb634a200ee9488d29c010ab3e8f57f43a..afa11a4e8ea6cd0ae62820ee825a64e3708c1db2 100644
--- a/src/ffi.rs
+++ b/src/ffi.rs
@@ -84,7 +84,6 @@ pub type PrivateKeyWriteCallback = extern "C" fn(buf: *mut c_char, size: c_int,
                                                  rwflag: c_int, user_data: *mut c_void)
                                                  -> c_int;
 
-
 pub static CRYPTO_LOCK: c_int = 1;
 
 pub static MBSTRING_ASC:  c_int = MBSTRING_FLAG | 1;
@@ -189,6 +188,9 @@ extern {}
 #[link(name="wsock32")]
 extern { }
 
+/* Since the openssl BN_is_zero is sometimes a macro, this wrapper is necessary. */
+pub unsafe fn BN_is_zero(a: *mut BIGNUM) -> c_int { bn_is_zero(a) }
+
 extern "C" {
     pub fn ASN1_INTEGER_set(dest: *mut ASN1_INTEGER, value: c_long) -> c_int;
     pub fn ASN1_STRING_type_new(ty: c_int) -> *mut ASN1_STRING;
@@ -239,7 +241,9 @@ extern "C" {
     /* Comparisons on BIGNUMs */
     pub fn BN_cmp(a: *mut BIGNUM, b: *mut BIGNUM) -> c_int;
     pub fn BN_ucmp(a: *mut BIGNUM, b: *mut BIGNUM) -> c_int;
-    pub fn BN_is_zero(a: *mut BIGNUM) -> c_int;
+
+    /* Special import from native/bn_is_zero.c */
+    pub fn bn_is_zero(a: *mut BIGNUM) -> c_int;
 
     /* Prime handling */
     pub fn BN_generate_prime_ex(r: *mut BIGNUM, bits: c_int, safe: c_int, add: *mut BIGNUM, rem: *mut BIGNUM, cb: *const c_void) -> c_int;
@@ -418,3 +422,4 @@ extern "C" {
     pub fn i2d_RSAPrivateKey(k: *mut RSA, buf: *const *mut u8) -> c_int;
     pub fn d2i_RSAPrivateKey(k: *const *mut RSA, buf: *const *const u8, len: c_uint) -> *mut RSA;
 }
+