diff --git a/src/shared/install.c b/src/shared/install.c
index 71392f367..9972fd7e9 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -565,7 +565,7 @@ int unit_file_mask(
                 unsigned *n_changes) {
 
         char **i;
-        _cleanup_free_ char *prefix;
+        _cleanup_free_ char *prefix = NULL;
         int r;
 
         assert(scope >= 0);