diff --git a/test-all-native.sh b/test-all-native.sh
index bb88c59..dfb9eec 100755
--- a/test-all-native.sh
+++ b/test-all-native.sh
@@ -565,6 +565,8 @@ grep -F 'tests/gcode/linuxcnc_fractional_linenumbers.ngc' test-linuxcnc-source-l
 grep -F 'tests/gcode/linuxcnc_extended_linenumbers.ngc' test-linuxcnc-source-link.sh >/dev/null
 grep -F 'tests/gcode/linuxcnc_close_and_downcase_words.ngc' test-linuxcnc-source-link.sh >/dev/null
 grep -F 'tests/gcode/linuxcnc_percent_file_ignores_trailing.ngc' test-linuxcnc-source-link.sh >/dev/null
+grep -F 'linuxcnc_unclosed_comment_error|Unclosed comment found' test-linuxcnc-source-link.sh >/dev/null
+grep -F 'linuxcnc_nested_comment_error|Nested comment found' test-linuxcnc-source-link.sh >/dev/null
 
 for script in \
     test-native.sh \
diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index 2823f9c..241d439 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -1202,11 +1202,14 @@ done
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_read.cc read_text()
 # rejects EOF without the matching percent/program end and overlong file
 # lines; read_n_number() rejects malformed N-line numbers through
-# read_integer_unsigned().
+# read_integer_unsigned(); src/emc/rs274ngc/interp_internal.cc
+# close_and_downcase() rejects unclosed and nested parenthesis comments.
 read_text_error_cases=(
     "linuxcnc_file_ended_no_program_end_error|File ended with no percent sign"
     "linuxcnc_file_ended_no_percent_error|File ended with no percent sign"
     "linuxcnc_bad_n_number_format_error|Bad format unsigned integer"
+    "linuxcnc_unclosed_comment_error|Unclosed comment found"
+    "linuxcnc_nested_comment_error|Nested comment found"
 )
 for case in "${read_text_error_cases[@]}"; do
     fixture=${case%%|*}
diff --git a/tests/gcode/linuxcnc_nested_comment_error.ngc b/tests/gcode/linuxcnc_nested_comment_error.ngc
new file mode 100644
index 0000000..b279125
--- /dev/null
+++ b/tests/gcode/linuxcnc_nested_comment_error.ngc
@@ -0,0 +1,2 @@
+G21 G90
+G0 X1 (outer (inner))
diff --git a/tests/gcode/linuxcnc_unclosed_comment_error.ngc b/tests/gcode/linuxcnc_unclosed_comment_error.ngc
new file mode 100644
index 0000000..4484093
--- /dev/null
+++ b/tests/gcode/linuxcnc_unclosed_comment_error.ngc
@@ -0,0 +1,2 @@
+G21 G90
+G0 X1 (missing close