diff --git a/library/pkcs11.c b/library/pkcs11.c
index b71415a..b68d688 100644
--- a/library/pkcs11.c
+++ b/library/pkcs11.c
@@ -115,7 +115,7 @@
                        int mode, size_t *olen,
                        const unsigned char *input,
                        unsigned char *output,
-                       unsigned int output_max_len )
+                       size_t output_max_len )
 {
     size_t input_len, output_len;