diff --git a/openssl-sys/src/x509.rs b/openssl-sys/src/x509.rs
index a3bd9fb0e363103704a2e253a62547e66f2f9947..99956fb06e2c201f5f0bf0ef6adde6ac8f66c923 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;