diff --git a/lib/internal.h b/lib/internal.h
index aee5f27c..1f4dab59 100644
--- a/lib/internal.h
+++ b/lib/internal.h
@@ -58,7 +58,7 @@ struct volume_key {
 };
 
 struct volume_key *crypt_alloc_volume_key(size_t keylength, const char *key);
-struct volume_key *crypt_generate_volume_key(struct crypt_device *cd, unsigned keylength);
+struct volume_key *crypt_generate_volume_key(struct crypt_device *cd, size_t keylength);
 void crypt_free_volume_key(struct volume_key *vk);
 
 /* Device backend */
diff --git a/lib/volumekey.c b/lib/volumekey.c
index 8b442c44..1ecd29d0 100644
--- a/lib/volumekey.c
+++ b/lib/volumekey.c
@@ -54,7 +54,7 @@ void crypt_free_volume_key(struct volume_key *vk)
 	}
 }
 
-struct volume_key *crypt_generate_volume_key(struct crypt_device *cd, unsigned keylength)
+struct volume_key *crypt_generate_volume_key(struct crypt_device *cd, size_t keylength)
 {
 	int r;
 	struct volume_key *vk;