diff --git a/docs/linuxcnc-porting.md b/docs/linuxcnc-porting.md
index 1a1b3f8..1e3377f 100644
--- a/docs/linuxcnc-porting.md
+++ b/docs/linuxcnc-porting.md
@@ -211,10 +211,10 @@ This matrix tracks LinuxCNC feature coverage for the web/WASM simulator. A featu
 | Coordinate offset Canon events `G10 L2`, `G10 L20`, `G10 P0 active-system targeting`, `G54`-`G59.3` selection, `G52`, `G92/G92.1/G92.2/G92.3` | covered through LinuxCNC native/source backends, including all nine G5X indices | `tests/gcode/linuxcnc_coordinate_offsets.ngc`, `tests/gcode/linuxcnc_coordinate_l20.ngc`, `tests/gcode/linuxcnc_coordinate_p0.ngc`, `tests/gcode/linuxcnc_coordinate_select_all.ngc`, `tests/gcode/linuxcnc_g92_restore.ngc`, `tests/gcode/linuxcnc_g52_offset.ngc` |
 | Cutter compensation | covered for tool-table `G41/G42 D...` and explicit-radius `G41.1/G42.1/G40` through LinuxCNC native/source backends | `tests/gcode/linuxcnc_cutter_comp.ngc` |
 | Probe moves `G38.2/G38.3/G38.4/G38.5` | covered as distinct probe events with LinuxCNC `probe_type` preserved through smoke, native, and source-linked paths | `tests/gcode/linuxcnc_probe_no_error.ngc` |
-| O-word subroutines, calls, and control flow | covered for numeric and named `O... sub/call/return/endsub` plus `if`/`elseif`/`else`, `while`, `repeat`, `do`/`while`, `break`, and `continue` through LinuxCNC file mode; source-linked read/execution errors cover malformed O-word commands, missing control-expression brackets, duplicate/undefined/unmatched labels, out-of-context `return`/`endsub`, wrong subroutine close style, too many call parameters, and Fanuc-style `M98` missing `P`; smoke parser also covers named `O<name>` sub/call/return/endsub and loop-control forms | `tests/gcode/smoke_oword_subprogram.ngc`, `tests/gcode/linuxcnc_named_oword_subprogram.ngc`, `tests/gcode/linuxcnc_oword_control_flow.ngc`, `tests/gcode/linuxcnc_oword_unknown_command_error.ngc`, `tests/gcode/linuxcnc_oword_unexpected_trailing_item_error.ngc`, `tests/gcode/linuxcnc_oword_if_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_elseif_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_while_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_repeat_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_too_many_call_parameters_error.ngc`, `tests/gcode/linuxcnc_oword_endsub_without_sub_error.ngc`, `tests/gcode/linuxcnc_oword_return_without_sub_error.ngc`, `tests/gcode/linuxcnc_oword_duplicate_if_label_error.ngc`, `tests/gcode/linuxcnc_oword_elseif_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_else_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_endif_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_break_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_continue_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_endwhile_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_elseif_no_matching_if_error.ngc`, `tests/gcode/linuxcnc_oword_break_no_matching_loop_error.ngc`, `tests/gcode/linuxcnc_oword_continue_no_matching_loop_error.ngc`, `tests/gcode/linuxcnc_oword_endrepeat_no_matching_repeat_error.ngc`, `tests/gcode/linuxcnc_oword_endif_no_matching_if_error.ngc`, `tests/gcode/linuxcnc_oword_endwhile_no_matching_while_error.ngc`, `tests/gcode/linuxcnc_oword_fanuc_requires_m99_error.ngc`, `tests/gcode/linuxcnc_oword_sub_requires_endsub_error.ngc`, `tests/gcode/linuxcnc_m98_missing_p_word_error.ngc` |
+| O-word subroutines, calls, and control flow | covered for numeric and named `O... sub/call/return/endsub` plus `if`/`elseif`/`else`, `while`, `repeat`, `do`/`while`, `break`, and `continue` through LinuxCNC file mode; source-linked read/execution errors cover malformed O-word commands, missing control-expression brackets, duplicate/undefined/unmatched labels, out-of-context `return`/`endsub`, wrong subroutine close style, too many call parameters, Fanuc-style `M98` missing `P`, and comment-prefixed `M98` falling through to normal M-code handling; smoke parser also covers named `O<name>` sub/call/return/endsub and loop-control forms | `tests/gcode/smoke_oword_subprogram.ngc`, `tests/gcode/linuxcnc_named_oword_subprogram.ngc`, `tests/gcode/linuxcnc_oword_control_flow.ngc`, `tests/gcode/linuxcnc_oword_unknown_command_error.ngc`, `tests/gcode/linuxcnc_oword_unexpected_trailing_item_error.ngc`, `tests/gcode/linuxcnc_oword_if_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_elseif_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_while_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_repeat_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_oword_too_many_call_parameters_error.ngc`, `tests/gcode/linuxcnc_oword_endsub_without_sub_error.ngc`, `tests/gcode/linuxcnc_oword_return_without_sub_error.ngc`, `tests/gcode/linuxcnc_oword_duplicate_if_label_error.ngc`, `tests/gcode/linuxcnc_oword_elseif_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_else_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_endif_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_break_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_continue_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_endwhile_undefined_label_error.ngc`, `tests/gcode/linuxcnc_oword_elseif_no_matching_if_error.ngc`, `tests/gcode/linuxcnc_oword_break_no_matching_loop_error.ngc`, `tests/gcode/linuxcnc_oword_continue_no_matching_loop_error.ngc`, `tests/gcode/linuxcnc_oword_endrepeat_no_matching_repeat_error.ngc`, `tests/gcode/linuxcnc_oword_endif_no_matching_if_error.ngc`, `tests/gcode/linuxcnc_oword_endwhile_no_matching_while_error.ngc`, `tests/gcode/linuxcnc_oword_fanuc_requires_m99_error.ngc`, `tests/gcode/linuxcnc_oword_sub_requires_endsub_error.ngc`, `tests/gcode/linuxcnc_m98_missing_p_word_error.ngc`, `tests/gcode/linuxcnc_comment_prefixed_m98_error.ngc` |
 | Parameter expressions and operators | covered for parameter references, source-linked `mod`, `**`, logical, and relational operator precedence, plus LinuxCNC parameter-setting syntax, parameter index validation, named-parameter termination, real-number parsing, divide-by-zero, negative sqrt/power, infinity rejection, malformed `ATAN[]/[]`, unary operation syntax, `read_operation_unary()` unknown-word branches, `read_operation()` binary-operation prefix, unknown operation, and unclosed-expression error paths from `interp_read.cc`/`interp_execute.cc` | `tests/gcode/linuxcnc_parameter_expression_assignment.ngc`, `tests/gcode/linuxcnc_parameter_missing_equal_error.ngc`, `tests/gcode/linuxcnc_parameter_missing_value_error.ngc`, `tests/gcode/linuxcnc_parameter_number_out_of_range_error.ngc`, `tests/gcode/linuxcnc_parameter_reference_out_of_range_error.ngc`, `tests/gcode/linuxcnc_non_integer_parameter_index_error.ngc`, `tests/gcode/linuxcnc_named_parameter_not_terminated_error.ngc`, `tests/gcode/linuxcnc_no_real_value_error.ngc`, `tests/gcode/linuxcnc_bad_number_format_error.ngc`, `tests/gcode/linuxcnc_expression_operators.ngc`, `tests/gcode/linuxcnc_negative_sqrt_error.ngc`, `tests/gcode/linuxcnc_divide_by_zero_error.ngc`, `tests/gcode/linuxcnc_negative_power_error.ngc`, `tests/gcode/linuxcnc_infinite_expression_error.ngc`, `tests/gcode/linuxcnc_atan_missing_slash_error.ngc`, `tests/gcode/linuxcnc_atan_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_unary_missing_bracket_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_c_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_e_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_f_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_l_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_r_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_s_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_t_word_error.ngc`, `tests/gcode/linuxcnc_unary_unknown_default_word_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_a_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_e_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_g_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_l_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_m_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_n_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_o_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_x_operation_error.ngc`, `tests/gcode/linuxcnc_binary_unknown_operation_error.ngc`, `tests/gcode/linuxcnc_unclosed_expression_error.ngc` |
 | Word reader validation | source-linked LinuxCNC reader errors covered for negative `F/G/H/L/M/S/T` values and repeated `A/B/C/D/E/F/H/I/J/K/L/P/Q/R/S/T/U/V/W/X/Y/Z` words from `interp_read.cc` | `tests/gcode/linuxcnc_negative_f_word_error.ngc`, `tests/gcode/linuxcnc_negative_g_code_error.ngc`, `tests/gcode/linuxcnc_negative_h_word_error.ngc`, `tests/gcode/linuxcnc_negative_l_word_error.ngc`, `tests/gcode/linuxcnc_negative_m_code_error.ngc`, `tests/gcode/linuxcnc_negative_s_word_error.ngc`, `tests/gcode/linuxcnc_negative_t_word_error.ngc`, `tests/gcode/linuxcnc_multiple_a_words_error.ngc`, `tests/gcode/linuxcnc_multiple_b_words_error.ngc`, `tests/gcode/linuxcnc_multiple_c_words_error.ngc`, `tests/gcode/linuxcnc_multiple_d_words_error.ngc`, `tests/gcode/linuxcnc_multiple_e_words_error.ngc`, `tests/gcode/linuxcnc_multiple_f_words_error.ngc`, `tests/gcode/linuxcnc_multiple_h_words_error.ngc`, `tests/gcode/linuxcnc_multiple_i_words_error.ngc`, `tests/gcode/linuxcnc_multiple_j_words_error.ngc`, `tests/gcode/linuxcnc_multiple_k_words_error.ngc`, `tests/gcode/linuxcnc_multiple_l_words_error.ngc`, `tests/gcode/linuxcnc_multiple_p_words_error.ngc`, `tests/gcode/linuxcnc_multiple_q_words_error.ngc`, `tests/gcode/linuxcnc_multiple_r_words_error.ngc`, `tests/gcode/linuxcnc_multiple_s_words_error.ngc`, `tests/gcode/linuxcnc_multiple_t_words_error.ngc`, `tests/gcode/linuxcnc_multiple_u_words_error.ngc`, `tests/gcode/linuxcnc_multiple_v_words_error.ngc`, `tests/gcode/linuxcnc_multiple_w_words_error.ngc`, `tests/gcode/linuxcnc_multiple_x_words_error.ngc`, `tests/gcode/linuxcnc_multiple_y_words_error.ngc`, `tests/gcode/linuxcnc_multiple_z_words_error.ngc` |
 | G/M reader validation | source-linked LinuxCNC `read_g()`/`read_m()` errors covered for range checks, unknown code tables, and same-modal-group conflicts from `interp_read.cc` and `interp_array.cc` | `tests/gcode/linuxcnc_g_code_out_of_range_error.ngc`, `tests/gcode/linuxcnc_unknown_g_code_error.ngc`, `tests/gcode/linuxcnc_two_g_codes_same_modal_group_error.ngc`, `tests/gcode/linuxcnc_m_code_greater_199_error.ngc`, `tests/gcode/linuxcnc_unknown_m_code_error.ngc`, `tests/gcode/linuxcnc_two_m_codes_same_modal_group_error.ngc` |
-| Block/item reader validation | source-linked LinuxCNC block reader errors covered for repeated `$`, bad item-start characters, middle-of-line `N` words, malformed leading `N` numbers, EOF/program-end file checks, overlong file lines, and too many M-codes from `interp_read.cc`, `interp_array.cc`, and `interp_check.cc` | `tests/gcode/linuxcnc_multiple_spindle_choice_words_error.ngc`, `tests/gcode/linuxcnc_bad_character_bang_error.ngc`, `tests/gcode/linuxcnc_bad_character_middle_n_word_error.ngc`, `tests/gcode/linuxcnc_bad_n_number_format_error.ngc`, `tests/gcode/linuxcnc_file_ended_no_program_end_error.ngc`, `tests/gcode/linuxcnc_file_ended_no_percent_error.ngc`, generated `linuxcnc_command_too_long_error.ngc`, `tests/gcode/linuxcnc_too_many_m_codes_error.ngc` |
+| Block/item reader validation | source-linked LinuxCNC block reader errors covered for repeated `$`, bad item-start characters, middle-of-line or comment-prefixed `N` words, comment-prefixed `O` words, malformed leading `N` numbers, EOF/program-end file checks, overlong file lines, and too many M-codes from `interp_read.cc`, `interp_array.cc`, and `interp_check.cc` | `tests/gcode/linuxcnc_multiple_spindle_choice_words_error.ngc`, `tests/gcode/linuxcnc_bad_character_bang_error.ngc`, `tests/gcode/linuxcnc_bad_character_middle_n_word_error.ngc`, `tests/gcode/linuxcnc_comment_prefixed_n_word_error.ngc`, `tests/gcode/linuxcnc_comment_prefixed_oword_error.ngc`, `tests/gcode/linuxcnc_bad_n_number_format_error.ngc`, `tests/gcode/linuxcnc_file_ended_no_program_end_error.ngc`, `tests/gcode/linuxcnc_file_ended_no_percent_error.ngc`, generated `linuxcnc_command_too_long_error.ngc`, `tests/gcode/linuxcnc_too_many_m_codes_error.ngc` |
 | Broader canned cycles `G73`, `G74`, `G82`-`G89` | partially covered: `G73`, `G74`, `G82`, `G83`, `G84`, `G85`, `G86`, `G87`, `G88`, `G89`; smoke parser maps supported cycles across `G17/G18/G19`, including LinuxCNC's special non-XY `G74/G84` tapping argument order and `G87` plane-specific `I/J/K` mapping; native/source regressions now check non-XY `G74/G84/G86/G87/G88` sequences | `tests/gcode/linuxcnc_canned_cycles_extended.ngc`, `tests/gcode/linuxcnc_canned_cycle_planes.ngc`, smoke API regression |
 | Full source-level wasm build | covered for the current wasm-safe RS274 source set, with remaining work focused on broadening browser-hostile dependency replacement and feature coverage | `./build-wasm.sh`, `test-linuxcnc-wasm-runtime-link.sh`, `test-web-wasm-node-smoke.sh`, `test-web-wasm-browser-smoke.sh` |
diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index f21a405..7c838e9 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -765,11 +765,15 @@ fi
 grep -Fq "Multiple spindle choice (\$) words on one line" \
     "$output_dir/cnc_sim_linuxcnc_source_multiple_spindle_choice_words_error.err"
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_read.cc
-# read_one_item() uses the default reader table from interp_array.cc and
-# rejects unknown item-start characters, including middle-of-line N words.
+# read_items() only consumes a leading N word before item dispatch;
+# read_one_item() then uses the default reader table from interp_array.cc
+# and rejects unknown item-start characters, including middle-of-line or
+# comment-prefixed N/O words.
 bad_character_error_cases=(
     "linuxcnc_bad_character_bang_error|Bad character '!' used"
     "linuxcnc_bad_character_middle_n_word_error|Bad character 'n' used"
+    "linuxcnc_comment_prefixed_n_word_error|Bad character 'n' used"
+    "linuxcnc_comment_prefixed_oword_error|Bad character 'o' used"
 )
 for case in "${bad_character_error_cases[@]}"; do
     fixture=${case%%|*}
@@ -881,6 +885,7 @@ oword_reader_error_cases=(
     "linuxcnc_oword_repeat_missing_bracket_error|Left bracket missing after 'repeat'"
     "linuxcnc_oword_too_many_call_parameters_error|Too many subroutine parameters"
     "linuxcnc_m98_missing_p_word_error|Found 'm98' code with no P-word"
+    "linuxcnc_comment_prefixed_m98_error|Unknown m code used: M98"
 )
 for case in "${oword_reader_error_cases[@]}"; do
     fixture=${case%%|*}
diff --git a/tests/gcode/linuxcnc_comment_prefixed_m98_error.ngc b/tests/gcode/linuxcnc_comment_prefixed_m98_error.ngc
new file mode 100644
index 0000000..35c28db
--- /dev/null
+++ b/tests/gcode/linuxcnc_comment_prefixed_m98_error.ngc
@@ -0,0 +1,6 @@
+G21
+F100
+(comment) M98 P100
+M30
+O100
+M99
diff --git a/tests/gcode/linuxcnc_comment_prefixed_n_word_error.ngc b/tests/gcode/linuxcnc_comment_prefixed_n_word_error.ngc
new file mode 100644
index 0000000..4f7462b
--- /dev/null
+++ b/tests/gcode/linuxcnc_comment_prefixed_n_word_error.ngc
@@ -0,0 +1,3 @@
+G21 G90 F100
+(comment) N10 G1 X5
+M30
diff --git a/tests/gcode/linuxcnc_comment_prefixed_oword_error.ngc b/tests/gcode/linuxcnc_comment_prefixed_oword_error.ngc
new file mode 100644
index 0000000..ae7144c
--- /dev/null
+++ b/tests/gcode/linuxcnc_comment_prefixed_oword_error.ngc
@@ -0,0 +1,3 @@
+G21 G90 F100
+(comment) O100
+M30