diff --git a/sys/net/if_fwsubr.c b/sys/net/if_fwsubr.c
index e004c4b5989c..331f361466f8 100644
--- a/sys/net/if_fwsubr.c
+++ b/sys/net/if_fwsubr.c
@@ -328,6 +328,8 @@ firewire_input_fragment(struct fw_com *fc, struct mbuf *m, int src)
 	int fstart, fend, start, end, islast;
 	uint32_t id;
 
+	GIANT_REQUIRED;
+
 	/*
 	 * Find an existing reassembly buffer or create a new one.
 	 */