diff --git a/test-all-native.sh b/test-all-native.sh
index 8b6ee28..17d1a5d 100755
--- a/test-all-native.sh
+++ b/test-all-native.sh
@@ -563,6 +563,7 @@ grep -F 'tests/gcode/linuxcnc_readonly_named_parameters.ngc' test-native.sh >/de
 grep -F 'read_n_number()' test-linuxcnc-source-link.sh >/dev/null
 grep -F 'tests/gcode/linuxcnc_fractional_linenumbers.ngc' test-linuxcnc-source-link.sh >/dev/null
 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
 
 for script in \
     test-native.sh \
diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index 1fa62ba..a7c0108 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -1495,6 +1495,12 @@ CNC_SIM_RS274_VAR="$var_file" \
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_extended_linenumbers.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_extended_linenumbers.json"
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_read.cc read_text()
+# calls close_and_downcase() to downcase words and remove spaces/tabs outside
+# comments before read_items() dispatches the words.
+CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_close_and_downcase_words.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_source_close_and_downcase_words.json"
 
 CNC_SIM_RS274_SOURCE_OUTPUT_DIR="$output_dir" python3 - <<'PY'
 import json
@@ -1556,6 +1562,16 @@ if extended_spindle_states[:3] != [(1, 111), (2, 222), (3, 333)]:
         f"{extended_spindle_states!r}"
     )
 
+close_and_downcase_words = load("cnc_sim_linuxcnc_source_close_and_downcase_words.json")
+if not any(
+    event["type"] == "linear-feed" and
+    event["line"] == 3 and
+    event["end"]["x"] == 3 and
+    event["end"]["y"] == 4
+    for event in close_and_downcase_words
+):
+    raise SystemExit("missing source-linked close_and_downcase mixed-case spaced-word move")
+
 block_delete_off = load("cnc_sim_linuxcnc_source_block_delete_off.json")
 if not any(
     event["type"] == "linear-feed" and event["line"] == 2 and event["end"]["x"] == 5
@@ -3444,3 +3460,4 @@ echo "dumped $output_dir/cnc_sim_linuxcnc_source_g52_xz_nurbs.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_g62_xz_nurbs.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_fractional_linenumbers.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_extended_linenumbers.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_source_close_and_downcase_words.json"
diff --git a/tests/gcode/linuxcnc_close_and_downcase_words.ngc b/tests/gcode/linuxcnc_close_and_downcase_words.ngc
new file mode 100644
index 0000000..48cf589
--- /dev/null
+++ b/tests/gcode/linuxcnc_close_and_downcase_words.ngc
@@ -0,0 +1,4 @@
+G 21 G 90 G 17
+F 100
+g 1 x 3 y 4
+M2