diff --git a/openssl/src/ssl/mod.rs b/openssl/src/ssl/mod.rs
index 01d652200eb2929403b690d5742a27c85f58465c..d47915b2fb041ef6928e22633fc2172336f7a36f 100644
--- a/openssl/src/ssl/mod.rs
+++ b/openssl/src/ssl/mod.rs
@@ -423,9 +423,9 @@ impl SslContext {
         }
     }
 
-    pub fn set_read_ahead(&self, m: c_long) {
+    pub fn set_read_ahead(&self, m: u32) {
         unsafe {
-            ffi::SSL_CTX_set_read_ahead(*self.ctx, m);
+            ffi::SSL_CTX_set_read_ahead(*self.ctx, m as c_long);
         }
     }