diff --git a/pd-mapper.c b/pd-mapper.c
index f5d45ee..10fe039 100644
--- a/pd-mapper.c
+++ b/pd-mapper.c
@@ -242,6 +242,8 @@ static int pd_enumerate_jsons(struct assoc *json_set)
 			continue;
 		}
 
+		firmware_value[n] = '\0';
+
 		if (strlen(FIRMWARE_BASE) + strlen(firmware_value) + 1 > sizeof(path))
 			continue;