diff --git a/include/security/pam_appl.h b/include/security/pam_appl.h
index f3e7e60..7fcc068 100644
--- a/include/security/pam_appl.h
+++ b/include/security/pam_appl.h
@@ -71,7 +71,7 @@ pam_end(pam_handle_t *_pamh,
 int
 pam_get_data(pam_handle_t *_pamh,
 	const char *_module_data_name,
-	void **_data);
+	const void **_data);
 
 int
 pam_get_item(pam_handle_t *_pamh,
diff --git a/lib/pam_get_data.c b/lib/pam_get_data.c
index 8b2b090..f258de8 100644
--- a/lib/pam_get_data.c
+++ b/lib/pam_get_data.c
@@ -50,7 +50,7 @@
 int
 pam_get_data(pam_handle_t *pamh,
 	const char *module_data_name,
-	void **data)
+	const void **data)
 {
 	pam_data_t *dp;