diff --git a/openssl-sys/src/lib.rs b/openssl-sys/src/lib.rs
index 0644a674d955b40ace038f52c790088ad2e5e5b3..1faf749eddc8d738dc1e23602d0331865993d645 100644
--- a/openssl-sys/src/lib.rs
+++ b/openssl-sys/src/lib.rs
@@ -361,6 +361,7 @@ extern "C" {
     pub fn HMAC_Init_ex(ctx: *mut HMAC_CTX, key: *const u8, keylen: c_int, md: *const EVP_MD, imple: *const ENGINE);
     pub fn HMAC_Final(ctx: *mut HMAC_CTX, output: *mut u8, len: *mut c_uint);
     pub fn HMAC_Update(ctx: *mut HMAC_CTX, input: *const u8, len: c_uint);
+    pub fn HMAC_CTX_cleanup(ctx: *mut HMAC_CTX);
 
 
     pub fn PEM_read_bio_X509(bio: *mut BIO, out: *mut *mut X509, callback: Option<PasswordCallback>,
diff --git a/src/crypto/hmac.rs b/src/crypto/hmac.rs
index a7a854b7a72371044300e8e2f09f6496ecc3c42b..8096a9480641effbee6bd23553fd3c0cd48dda81 100644
--- a/src/crypto/hmac.rs
+++ b/src/crypto/hmac.rs
@@ -61,6 +61,14 @@ impl HMAC {
     }
 }
 
+impl Drop for HMAC {
+    fn drop(&mut self) {
+        unsafe {
+            ffi::HMAC_CTX_cleanup(&mut self.ctx);
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use serialize::hex::FromHex;