diff --git a/vhdl/splink.vhdl b/vhdl/splink.vhdl
index cf585da..ccd3062 100644
--- a/vhdl/splink.vhdl
+++ b/vhdl/splink.vhdl
@@ -146,10 +146,12 @@ begin
 						-- TODO udp_length, range check with MAX_STRAND_LEN
 						num_pixels <= MAX_STRAND_LEN;
 
-						-- FIXME bounds check
-						active_strand <= to_integer(unsigned(udp_data));
-
-						receive_state <= FRAME_NUM;
+						if unsigned(udp_data) >= NUM_STRANDS then
+							receive_state <= DROP;
+						else
+							active_strand <= to_integer(unsigned(udp_data));
+							receive_state <= FRAME_NUM;
+						end if;
 
 					when FRAME_NUM =>
 						if not some_strands_written then