diff --git a/vunit/vhdl/verification_components/src/axi_stream_protocol_checker.vhd b/vunit/vhdl/verification_components/src/axi_stream_protocol_checker.vhd
index 49b49c84e5..d9f81cb5e1 100644
--- a/vunit/vhdl/verification_components/src/axi_stream_protocol_checker.vhd
+++ b/vunit/vhdl/verification_components/src/axi_stream_protocol_checker.vhd
@@ -69,6 +69,20 @@ architecture a of axi_stream_protocol_checker is
   signal areset_n_d  : std_logic := '0';
   signal areset_rose : std_logic;
   signal not_tvalid  : std_logic;
+
+  signal tdata_masked : std_logic_vector(tdata'range);
+
+  function mask_unused_bytes(data : std_logic_vector; keep : std_logic_vector) return std_logic_vector is
+    variable ret : std_logic_vector(data'range);
+  begin
+    ret := data;
+    for i in keep'range loop
+      if keep(i) = '0' then
+        ret(i*8+7 downto i*8) := (others => '0');
+      end if;
+    end loop;
+    return ret;
+  end function;
 begin
   handshake_is_not_x <= '1' when not is_x(tvalid) and not is_x(tready) else '0';
 
@@ -112,7 +126,8 @@ begin
 
   -- AXI4STREAM_ERRM_TDATA_X A value of X on TDATA is not permitted when TVALID
   -- is HIGH
-  check_not_unknown(rule5_checker, aclk, tvalid, tdata, result("for tdata when tvalid is high"));
+  tdata_masked <= mask_unused_bytes(tdata, tkeep);
+  check_not_unknown(rule5_checker, aclk, tvalid, tdata_masked, result("for tdata when tvalid is high"));
 
   -- AXI4STREAM_ERRM_TLAST_X A value of X on TLAST is not permitted when TVALID
   -- is HIGH