diff --git a/openssl-sys/src/x509.rs b/openssl-sys/src/x509.rs
index a3bd9fb0..99956fb0 100644
--- a/openssl-sys/src/x509.rs
+++ b/openssl-sys/src/x509.rs
@@ -74,7 +74,7 @@ cfg_if! {
 
 stack!(stack_st_X509);
 
-pub type X509_LOOKUP_TYPE = i32;
+pub type X509_LOOKUP_TYPE = u32;
 pub const X509_LU_NONE: X509_LOOKUP_TYPE = 0;
 pub const X509_LU_X509: X509_LOOKUP_TYPE = 1;
 pub const X509_LU_CRL: X509_LOOKUP_TYPE = 2;