diff --git a/scripts/policy/protocols/modbus/track-memmap.bro b/scripts/policy/protocols/modbus/track-memmap.bro
index cc02ce9e6a..fc02d9b274 100644
--- a/scripts/policy/protocols/modbus/track-memmap.bro
+++ b/scripts/policy/protocols/modbus/track-memmap.bro
@@ -60,7 +60,7 @@ event modbus_read_holding_registers_request(c: connection, headers: ModbusHeader
 	c$modbus$track_address = start_address+1;
 	}
 
-event modbus_read_holding_registers_response(c: connection, headers: ModbusHeaders, byte_count: count, registers: ModbusRegisters)
+event modbus_read_holding_registers_response(c: connection, headers: ModbusHeaders, registers: ModbusRegisters)
 	{
 	local slave = c$id$resp_h;
 
diff --git a/src/event.bif b/src/event.bif
index cc8acb1849..b965c26ae9 100644
--- a/src/event.bif
+++ b/src/event.bif
@@ -6623,10 +6623,8 @@ event modbus_read_holding_registers_request%(c: connection, headers: ModbusHeade
 ##
 ## headers: The headers for the modbus function.
 ##
-## byte_count: The number of bytes in the message that comprise register values.
-##
 ## registers: The register values returned from the device.
-event modbus_read_holding_registers_response%(c: connection, headers: ModbusHeaders, byte_count: count, registers: ModbusRegisters%);
+event modbus_read_holding_registers_response%(c: connection, headers: ModbusHeaders, registers: ModbusRegisters%);
 
 ## Generated for a Modbus read input registers request.
 ##
@@ -6645,10 +6643,8 @@ event modbus_read_input_registers_request%(c: connection, headers: ModbusHeaders
 ##
 ## headers: The headers for the modbus function.
 ##
-## byte_count: The number of bytes in the message that comprise register values.
-##
 ## registers: The register values returned from the device.
-event modbus_read_input_registers_response%(c: connection, headers: ModbusHeaders, byte_count: count, registers: ModbusRegisters%);
+event modbus_read_input_registers_response%(c: connection, headers: ModbusHeaders, registers: ModbusRegisters%);
 
 ## Generated for a Modbus write single coil request.
 ##
@@ -6724,10 +6720,8 @@ event modbus_write_multiple_coils_response%(c: connection, headers: ModbusHeader
 ##
 ## start_address: The memory address of the first register to be written.
 ##
-## byte_count: The number of bytes in the message that comprise register values.
-##
 ## registers: The values to be written to the registers.
-event modbus_write_multiple_registers_request%(c: connection, headers: ModbusHeaders, start_address: count, byte_count: count, registers: ModbusRegisters%);
+event modbus_write_multiple_registers_request%(c: connection, headers: ModbusHeaders, start_address: count, registers: ModbusRegisters%);
 
 ## Generated for a Modbus write multiple registers response.
 ##
@@ -6818,10 +6812,8 @@ event modbus_mask_write_register_response%(c: connection, headers: ModbusHeaders
 ##
 ## write_start_address: The memory address of the first register to be written.
 ##
-## write_byte_count: Number of bytes in message that comprise register values.
-##
 ## write_registers: The values to be written to the registers.
-event modbus_read_write_multiple_registers_request%(c: connection, headers: ModbusHeaders, read_start_address: count, read_quantity: count, write_start_address: count, write_byte_count: count, write_registers: ModbusRegisters%);
+event modbus_read_write_multiple_registers_request%(c: connection, headers: ModbusHeaders, read_start_address: count, read_quantity: count, write_start_address: count, write_registers: ModbusRegisters%);
 
 ## Generated for a Modbus read/write multiple registers response.
 ##
@@ -6829,10 +6821,8 @@ event modbus_read_write_multiple_registers_request%(c: connection, headers: Modb
 ##
 ## headers: The headers for the modbus function.
 ##
-## byte_count: The number of bytes in the message that comprise register values.
-##
 ## written_registers: The register values read from the registers specified in the request.
-event modbus_read_write_multiple_registers_response%(c: connection, headers: ModbusHeaders, byte_count: count, written_registers: ModbusRegisters%);
+event modbus_read_write_multiple_registers_response%(c: connection, headers: ModbusHeaders, written_registers: ModbusRegisters%);
 
 ## Generated for a Modbus read FIFO queue request.
 ##
@@ -6849,10 +6839,8 @@ event modbus_read_fifo_queue_request%(c: connection, headers: ModbusHeaders, sta
 ##
 ## headers: The headers for the modbus function.
 ##
-## byte_count: The number of bytes in the message that comprise register values.
-##
 ## fifos: The register values read from the FIFO queue on the device.
-event modbus_read_fifo_queue_response%(c: connection, headers: ModbusHeaders, byte_count: count, fifos: ModbusRegisters%);
+event modbus_read_fifo_queue_response%(c: connection, headers: ModbusHeaders, fifos: ModbusRegisters%);
 
 ## Raised for informational messages reported via Bro's reporter framework. Such
 ## messages may be generated internally by the event engine and also by other
diff --git a/src/modbus-analyzer.pac b/src/modbus-analyzer.pac
index 155da9647f..b03df9d188 100644
--- a/src/modbus-analyzer.pac
+++ b/src/modbus-analyzer.pac
@@ -135,8 +135,16 @@ refine flow ModbusTCP_Flow += {
 	# RESPONSE FC=3
 	function deliver_ReadHoldingRegistersResponse(header: ModbusTCP_TransportHeader, message: ReadHoldingRegistersResponse): bool
 		%{
+		if ( ${message.byte_count} % 2 != 0 )
+			{
+			connection()->bro_analyzer()->ProtocolViolation(
+			    fmt("invalid value for modbus read holding register response byte count %d", ${message.byte_count}));
+			return false;
+			}
+
 		if ( ::modbus_read_holding_registers_response )
 			{
+
 			VectorVal* t = new VectorVal(BifType::Vector::ModbusRegisters);
 			for ( unsigned int i=0; i < ${message.registers}->size(); ++i )
 				{
@@ -147,7 +155,6 @@ refine flow ModbusTCP_Flow += {
 			BifEvent::generate_modbus_read_holding_registers_response(connection()->bro_analyzer(),
 			                                                          connection()->bro_analyzer()->Conn(),
 			                                                          HeaderToBro(header),
-			                                                          ${message.byte_count},
 			                                                          t);
 			}
 
@@ -172,6 +179,13 @@ refine flow ModbusTCP_Flow += {
 	# RESPONSE FC=4
 	function deliver_ReadInputRegistersResponse(header: ModbusTCP_TransportHeader, message: ReadInputRegistersResponse): bool
 		%{
+		if ( ${message.byte_count} % 2 != 0 )
+			{
+			connection()->bro_analyzer()->ProtocolViolation(
+			    fmt("invalid value for modbus read input register response byte count %d", ${message.byte_count}));
+			return false;
+			}
+
 		if ( ::modbus_read_input_registers_response )
 			{
 			VectorVal* t = new VectorVal(BifType::Vector::ModbusRegisters);
@@ -184,7 +198,6 @@ refine flow ModbusTCP_Flow += {
 			BifEvent::generate_modbus_read_input_registers_response(connection()->bro_analyzer(),
 			                                                        connection()->bro_analyzer()->Conn(),
 			                                                        HeaderToBro(header),
-			                                                        ${message.byte_count},
 			                                                        t);
 			}
 
@@ -309,6 +322,13 @@ refine flow ModbusTCP_Flow += {
 	# REQUEST FC=16
 	function deliver_WriteMultipleRegistersRequest(header: ModbusTCP_TransportHeader, message: WriteMultipleRegistersRequest): bool
 		%{
+		if ( ${message.byte_count} % 2 != 0 )
+			{
+			connection()->bro_analyzer()->ProtocolViolation(
+			    fmt("invalid value for modbus write multiple registers request byte count %d", ${message.byte_count}));
+			return false;
+			}
+
 		if ( ::modbus_write_multiple_registers_request )
 			{
 			VectorVal * t = new VectorVal(BifType::Vector::ModbusRegisters);
@@ -321,7 +341,7 @@ refine flow ModbusTCP_Flow += {
 				BifEvent::generate_modbus_write_multiple_registers_request(connection()->bro_analyzer(),
 				                                                           connection()->bro_analyzer()->Conn(),
 				                                                           HeaderToBro(header),
-				                                                           ${message.start_address}, ${message.byte_count}, t);
+				                                                           ${message.start_address}, t);
 			}
 
 		return true;
@@ -486,6 +506,13 @@ refine flow ModbusTCP_Flow += {
 	# REQUEST FC=23
 	function deliver_ReadWriteMultipleRegistersRequest(header: ModbusTCP_TransportHeader, message: ReadWriteMultipleRegistersRequest): bool
 		%{
+		if ( ${message.write_byte_count} % 2 != 0 )
+			{
+			connection()->bro_analyzer()->ProtocolViolation(
+			    fmt("invalid value for modbus read write multiple registers request write byte count %d", ${message.write_byte_count}));
+			return false;
+			}
+
 		if ( ::modbus_read_write_multiple_registers_request )
 			{
 			VectorVal* t = new VectorVal(BifType::Vector::ModbusRegisters);
@@ -501,7 +528,6 @@ refine flow ModbusTCP_Flow += {
 			                                                                ${message.read_start_address},
 			                                                                ${message.read_quantity},
 			                                                                ${message.write_start_address},
-			                                                                ${message.write_byte_count},
 			                                                                t);
 			}
 
@@ -511,6 +537,13 @@ refine flow ModbusTCP_Flow += {
 	# RESPONSE FC=23
 	function deliver_ReadWriteMultipleRegistersResponse(header: ModbusTCP_TransportHeader, message: ReadWriteMultipleRegistersResponse): bool
 		%{
+		if ( ${message.byte_count} % 2 != 0 )
+			{
+			connection()->bro_analyzer()->ProtocolViolation(
+			    fmt("invalid value for modbus read write multiple registers response byte count %d", ${message.byte_count}));
+			return false;
+			}
+
 		if ( ::modbus_read_write_multiple_registers_response )
 			{
 			VectorVal* t = new VectorVal(BifType::Vector::ModbusRegisters);
@@ -523,7 +556,6 @@ refine flow ModbusTCP_Flow += {
 			BifEvent::generate_modbus_read_write_multiple_registers_response(connection()->bro_analyzer(),
 			                                                                 connection()->bro_analyzer()->Conn(),
 			                                                                 HeaderToBro(header),
-			                                                                 ${message.byte_count},
 			                                                                 t);
 			}
 
@@ -548,6 +580,13 @@ refine flow ModbusTCP_Flow += {
 	# RESPONSE FC=24
 	function deliver_ReadFIFOQueueResponse(header: ModbusTCP_TransportHeader, message: ReadFIFOQueueResponse): bool
 		%{
+		if ( ${message.byte_count} % 2 != 0 )
+			{
+			connection()->bro_analyzer()->ProtocolViolation(
+			    fmt("invalid value for modbus read FIFO queue response byte count %d", ${message.byte_count}));
+			return false;
+			}
+
 		if ( ::modbus_read_fifo_queue_response )
 			{
 			VectorVal* t = new VectorVal(new VectorType(base_type(TYPE_COUNT)));
@@ -560,7 +599,6 @@ refine flow ModbusTCP_Flow += {
 			BifEvent::generate_modbus_read_fifo_queue_response(connection()->bro_analyzer(),
 			                                                   connection()->bro_analyzer()->Conn(),
 			                                                   HeaderToBro(header),
-			                                                   ${message.byte_count},
 			                                                   t);
 			}
 
diff --git a/testing/btest/Baseline/scripts.base.protocols.modbus.register_parsing/output b/testing/btest/Baseline/scripts.base.protocols.modbus.register_parsing/output
index 353f85d2ef..5bb5f1be7c 100644
--- a/testing/btest/Baseline/scripts.base.protocols.modbus.register_parsing/output
+++ b/testing/btest/Baseline/scripts.base.protocols.modbus.register_parsing/output
@@ -1,5 +1,4 @@
 modbus_read_input_registers_request, [orig_h=10.1.1.234, orig_p=51411/tcp, resp_h=10.10.5.104, resp_p=502/tcp], [tid=1119, pid=0, uid=255, function_code=4], 900, 147
-modbus_read_input_registers_response, [orig_h=10.1.1.234, orig_p=51411/tcp, resp_h=10.10.5.104, resp_p=502/tcp], [tid=2606, pid=0, uid=255, function_code=4], [0, 0, 0, 0, 0, 0, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690], 100, 200
-modbus_read_input_registers_response, [orig_h=10.1.1.234, orig_p=51411/tcp, resp_h=10.10.5.104, resp_p=502/tcp], [tid=6714, pid=0, uid=255, function_code=4], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3840, 0, 0, 31, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 37, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], 64, 129
+modbus_read_input_registers_response, [orig_h=10.1.1.234, orig_p=51411/tcp, resp_h=10.10.5.104, resp_p=502/tcp], [tid=2606, pid=0, uid=255, function_code=4], [0, 0, 0, 0, 0, 0, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690], 100
 modbus_read_input_registers_request, [orig_h=10.1.1.234, orig_p=51411/tcp, resp_h=10.10.5.104, resp_p=502/tcp], [tid=12993, pid=0, uid=255, function_code=4], 400, 100
-modbus_read_input_registers_response, [orig_h=10.1.1.234, orig_p=51411/tcp, resp_h=10.10.5.104, resp_p=502/tcp], [tid=17667, pid=0, uid=255, function_code=4], [49, 18012, 51, 42, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 49, 50, 51, 54324, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 69, 63, 64, 65, 66, 67, 68, 49, 189, 51, 52, 53, 54, 4151, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 136, 49, 50, 51, 212, 53, 54, 170, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690], 100, 200
+modbus_read_input_registers_response, [orig_h=10.1.1.234, orig_p=51411/tcp, resp_h=10.10.5.104, resp_p=502/tcp], [tid=17667, pid=0, uid=255, function_code=4], [49, 18012, 51, 42, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 49, 50, 51, 54324, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 69, 63, 64, 65, 66, 67, 68, 49, 189, 51, 52, 53, 54, 4151, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 136, 49, 50, 51, 212, 53, 54, 170, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690, 43690], 100
diff --git a/testing/btest/scripts/base/protocols/modbus/events.bro b/testing/btest/scripts/base/protocols/modbus/events.bro
index 6c47dc611a..f648a0adde 100644
--- a/testing/btest/scripts/base/protocols/modbus/events.bro
+++ b/testing/btest/scripts/base/protocols/modbus/events.bro
@@ -41,7 +41,7 @@ event modbus_read_holding_registers_request(c: connection, headers: ModbusHeader
     print "modbus_read_holding_registers_request", c, headers, start_address, quantity;
 }
 
-event modbus_read_holding_registers_response(c: connection, headers: ModbusHeaders, byte_count: count, registers: ModbusRegisters)
+event modbus_read_holding_registers_response(c: connection, headers: ModbusHeaders, registers: ModbusRegisters)
 {
     print "modbus_read_holding_registers_response", c, headers, registers;
 }
@@ -51,7 +51,7 @@ event modbus_read_input_registers_request(c: connection, headers: ModbusHeaders,
     print "modbus_read_input_registers_request", c, headers, start_address, quantity;
 }
 
-event modbus_read_input_registers_response(c: connection, headers: ModbusHeaders, byte_count: count, registers: ModbusRegisters)
+event modbus_read_input_registers_response(c: connection, headers: ModbusHeaders, registers: ModbusRegisters)
 {
     print "modbus_read_input_registers_response", c, headers, registers;
 }
@@ -86,7 +86,7 @@ event modbus_write_multiple_coils_response(c: connection, headers: ModbusHeaders
     print "modbus_write_multiple_coils_response", c, headers, start_address, quantity;
 }
 
-event modbus_write_multiple_registers_request(c: connection, headers: ModbusHeaders, start_address: count, byte_count: count, registers: ModbusRegisters)
+event modbus_write_multiple_registers_request(c: connection, headers: ModbusHeaders, start_address: count, registers: ModbusRegisters)
 {
     print "modbus_write_multiple_registers_request", c, headers, start_address, registers;
 }
@@ -126,12 +126,12 @@ event modbus_mask_write_register_response(c: connection, headers: ModbusHeaders,
     print "modbus_mask_write_register_response", c, headers, address, and_mask, or_mask;
 }
 
-event modbus_read_write_multiple_registers_request(c: connection, headers: ModbusHeaders, read_start_address: count, read_quantity: count, write_start_address: count, write_byte_count: count, write_registers: ModbusRegisters)
+event modbus_read_write_multiple_registers_request(c: connection, headers: ModbusHeaders, read_start_address: count, read_quantity: count, write_start_address: count, write_registers: ModbusRegisters)
 {
     print "modbus_read_write_multiple_registers_request", c, headers, read_start_address, read_quantity, write_start_address, write_registers;
 }
 
-event modbus_read_write_multiple_registers_response(c: connection, headers: ModbusHeaders, byte_count: count, written_registers: ModbusRegisters)
+event modbus_read_write_multiple_registers_response(c: connection, headers: ModbusHeaders, written_registers: ModbusRegisters)
 {
     print "modbus_read_write_multiple_registers_response", c, headers, written_registers;
 }
@@ -141,7 +141,7 @@ event modbus_read_fifo_queue_request(c: connection, headers: ModbusHeaders, star
     print "modbus_read_fifo_queue_request", c, headers, start_address;
 }
 
-event modbus_read_fifo_queue_response(c: connection, headers: ModbusHeaders, byte_count: count, fifos: ModbusRegisters)
+event modbus_read_fifo_queue_response(c: connection, headers: ModbusHeaders, fifos: ModbusRegisters)
 {
     print "modbus_read_fifo_queue_response", c, headers, fifos;
 }
diff --git a/testing/btest/scripts/base/protocols/modbus/register_parsing.bro b/testing/btest/scripts/base/protocols/modbus/register_parsing.bro
index 300dd75bfe..1641860228 100644
--- a/testing/btest/scripts/base/protocols/modbus/register_parsing.bro
+++ b/testing/btest/scripts/base/protocols/modbus/register_parsing.bro
@@ -6,15 +6,16 @@
 # of register values, with the quantity being derived from a byte count value
 # that is also sent.  If the byte count value is invalid (e.g. an odd value
 # might not be valid since registers must be 2-byte values), then the parser
-# should not trigger any asserts, but the resulting event could indicate
-# the strangeness (i.e. byte_count != 2*|registers|).
+# should not trigger any asserts, but generate a protocol_violation (in this
+# case TCP_ApplicationAnalyzer::ProtocolViolation asserts its behavior for
+# incomplete connections).
 
 event modbus_read_input_registers_request(c: connection, headers: ModbusHeaders, start_address: count, quantity: count)
 	{
 	print "modbus_read_input_registers_request", c$id, headers, start_address, quantity;
 	}
 
-event modbus_read_input_registers_response(c: connection, headers: ModbusHeaders, byte_count: count, registers: ModbusRegisters)
+event modbus_read_input_registers_response(c: connection, headers: ModbusHeaders, registers: ModbusRegisters)
 	{
-	print "modbus_read_input_registers_response", c$id, headers, registers, |registers|, byte_count;
+	print "modbus_read_input_registers_response", c$id, headers, registers, |registers|;
 	}