diff --git a/nanomodbus.c b/nanomodbus.c
index 642d499..40784ee 100644
--- a/nanomodbus.c
+++ b/nanomodbus.c
@@ -1190,6 +1190,9 @@ static nmbs_error handle_read_file_record(nmbs_t* nmbs) {
             if (subreq[i].record_number > 0x270F)
                 return send_exception_msg(nmbs, NMBS_EXCEPTION_ILLEGAL_DATA_ADDRESS);
 
+            if (subreq[i].record_length > 124)
+                return send_exception_msg(nmbs, NMBS_EXCEPTION_ILLEGAL_DATA_ADDRESS);
+
             NMBS_DEBUG_PRINT("a %d\tr %d\tl %d\t fread ", subreq[i].file_number, subreq[i].record_number,
                              subreq[i].record_length);
         }
@@ -1259,7 +1262,7 @@ static nmbs_error handle_write_file_record(nmbs_t* nmbs) {
         uint16_t size = request_size;
         nmbs->msg.buf_idx = msg_buf_idx;    // restore context
 
-        if (request_size < 0x07 || request_size > 0xF5)
+        if (request_size < 0x07 || request_size > 0xFB)
             return send_exception_msg(nmbs, NMBS_EXCEPTION_ILLEGAL_DATA_VALUE);
 
         do {
@@ -1278,6 +1281,9 @@ static nmbs_error handle_write_file_record(nmbs_t* nmbs) {
             if (subreq_record_number_c > 0x270F)
                 return send_exception_msg(nmbs, NMBS_EXCEPTION_ILLEGAL_DATA_ADDRESS);
 
+            if (subreq_record_length_c > 122)
+                return send_exception_msg(nmbs, NMBS_EXCEPTION_ILLEGAL_DATA_ADDRESS);
+
             NMBS_DEBUG_PRINT("a %d\tr %d\tl %d\t fwrite ", subreq_file_number_c, subreq_record_number_c,
                              subreq_record_length_c);
             size -= (subreq_header_size + subreq_record_length_c * 2);
@@ -1652,6 +1658,9 @@ nmbs_error nmbs_read_file_record(nmbs_t* nmbs, uint16_t file_number, uint16_t re
     if (record_number > 0x270F)
         return NMBS_ERROR_INVALID_ARGUMENT;
 
+    if (count > 124)
+        return NMBS_ERROR_INVALID_ARGUMENT;
+
     msg_state_req(nmbs, 20);
     put_req_header(nmbs, 8);
 
@@ -1681,6 +1690,9 @@ nmbs_error nmbs_write_file_record(nmbs_t* nmbs, uint16_t file_number, uint16_t r
     if (record_number > 0x270F)
         return NMBS_ERROR_INVALID_ARGUMENT;
 
+    if (count > 122)
+        return NMBS_ERROR_INVALID_ARGUMENT;
+
     uint16_t data_size = count * 2;
 
     msg_state_req(nmbs, 21);
diff --git a/tests/nanomodbus_tests.c b/tests/nanomodbus_tests.c
index 0ca351a..885871e 100644
--- a/tests/nanomodbus_tests.c
+++ b/tests/nanomodbus_tests.c
@@ -842,8 +842,8 @@ nmbs_error read_file(uint16_t file_number, uint16_t record_number, uint16_t* reg
         registers[3] = 0xFFFF;
     }
 
-    if (file_number == 255 && record_number == 9999 && count == 119)
-        registers[118] = 42;
+    if (file_number == 255 && record_number == 9999 && count == 124)
+        registers[123] = 42;
 
     return NMBS_ERROR_NONE;
 }
@@ -868,6 +868,9 @@ void test_fc20(nmbs_transport transport) {
     should("immediately return NMBS_ERROR_INVALID_ARGUMENT when calling with record_number > 9999");
     expect(nmbs_read_file_record(&CLIENT, 1, 10000, registers, 1) == NMBS_ERROR_INVALID_ARGUMENT);
 
+    should("return NMBS_ERROR_INVALID_ARGUMENT when calling with count > 124");
+    expect(nmbs_read_file_record(&CLIENT, 1, 0, registers, 125) == NMBS_ERROR_INVALID_ARGUMENT);
+
     should("return NMBS_EXCEPTION_SERVER_DEVICE_FAILURE when server handler returns any non-exception error");
     expect(nmbs_read_file_record(&CLIENT, 1, 1, registers, 3) == NMBS_EXCEPTION_SERVER_DEVICE_FAILURE);
 
@@ -884,8 +887,8 @@ void test_fc20(nmbs_transport transport) {
     expect(registers[2] == 0xAA55);
     expect(registers[3] == 0xFFFF);
 
-    check(nmbs_read_file_record(&CLIENT, 255, 9999, registers, 119));
-    expect(registers[118] == 42);
+    check(nmbs_read_file_record(&CLIENT, 255, 9999, registers, 124));
+    expect(registers[123] == 42);
 
     stop_client_and_server();
 }
@@ -914,8 +917,8 @@ nmbs_error write_file(uint16_t file_number, uint16_t record_number, const uint16
         return NMBS_ERROR_NONE;
     }
 
-    if (file_number == 255 && record_number == 9999 && count == 119)
-        expect(registers[118] == 42);
+    if (file_number == 255 && record_number == 9999 && count == 122)
+        expect(registers[121] == 42);
 
     return NMBS_ERROR_NONE;
 }
@@ -937,9 +940,12 @@ void test_fc21(nmbs_transport transport) {
     should("immediately return NMBS_ERROR_INVALID_ARGUMENT when calling with file_number 0");
     expect(nmbs_write_file_record(&CLIENT, 0, 0, registers, 1) == NMBS_ERROR_INVALID_ARGUMENT);
 
-    should("immediately return NMBS_ERROR_INVALID_ARGUMENT when calling with record_number > 0x007B");
+    should("immediately return NMBS_ERROR_INVALID_ARGUMENT when calling with record_number > 9999");
     expect(nmbs_write_file_record(&CLIENT, 1, 10000, registers, 1) == NMBS_ERROR_INVALID_ARGUMENT);
 
+    should("return NMBS_ERROR_INVALID_ARGUMENT hen calling with count > 123");
+    expect(nmbs_write_file_record(&CLIENT, 1, 0, registers, 123) == NMBS_ERROR_INVALID_ARGUMENT);
+
     should("return NMBS_EXCEPTION_SERVER_DEVICE_FAILURE when server handler returns any non-exception error");
     expect(nmbs_write_file_record(&CLIENT, 1, 1, registers, 1) == NMBS_EXCEPTION_SERVER_DEVICE_FAILURE);
 
@@ -956,8 +962,8 @@ void test_fc21(nmbs_transport transport) {
     registers[3] = 0xFFFF;
     check(nmbs_write_file_record(&CLIENT, 4, 4, registers, 4));
 
-    registers[118] = 42;
-    check(nmbs_write_file_record(&CLIENT, 255, 9999, registers, 119));
+    registers[121] = 42;
+    check(nmbs_write_file_record(&CLIENT, 255, 9999, registers, 122));
 
     stop_client_and_server();
 }