diff --git a/test-all-native.sh b/test-all-native.sh
index f8b3534..10e69af 100755
--- a/test-all-native.sh
+++ b/test-all-native.sh
@@ -560,6 +560,8 @@ grep -F 'convert_lathe_diameter_mode() scales G7/G8 X words and G76 I/J/K words'
 grep -F 'tests/gcode/linuxcnc_lathe_diameter_mode.ngc' test-native.sh >/dev/null
 grep -F 'tests/gcode/linuxcnc_lathe_diameter_g76.ngc' test-native.sh >/dev/null
 grep -F 'tests/gcode/linuxcnc_readonly_named_parameters.ngc' test-native.sh >/dev/null
+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
 
 for script in \
     test-native.sh \
diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index 123b905..84b3b07 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -1484,6 +1484,13 @@ cp "$base_var_file" "$var_file"
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_g62_xz_nurbs.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_g62_xz_nurbs.json"
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_read.cc read_n_number()
+# accepts and ignores the fractional suffix after an N word; execute_block()
+# in src/emc/rs274ngc/interp_execute.cc still tags canon output with the
+# interpreter sequence number.
+CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_fractional_linenumbers.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_source_fractional_linenumbers.json"
 
 CNC_SIM_RS274_SOURCE_OUTPUT_DIR="$output_dir" python3 - <<'PY'
 import json
@@ -1521,6 +1528,18 @@ required_motion = {
 check_motion("cnc_sim_linuxcnc_source_basic_motion.json", required_motion)
 check_motion("cnc_sim_linuxcnc_source_basic_mill.json", required_motion | {"tool-change"})
 
+fractional_linenumbers = load("cnc_sim_linuxcnc_source_fractional_linenumbers.json")
+fractional_spindle_states = [
+    (event["line"], event["spindle"])
+    for event in fractional_linenumbers
+    if event["type"] == "set-spindle"
+]
+if fractional_spindle_states[:3] != [(1, 300), (2, 600), (3, 1200)]:
+    raise SystemExit(
+        "unexpected source-linked fractional N-word spindle sequence: "
+        f"{fractional_spindle_states!r}"
+    )
+
 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
@@ -3407,3 +3426,4 @@ echo "dumped $output_dir/cnc_sim_linuxcnc_source_g92_restore.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_g52_offset.json"
 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"
diff --git a/tests/gcode/linuxcnc_fractional_linenumbers.ngc b/tests/gcode/linuxcnc_fractional_linenumbers.ngc
new file mode 100644
index 0000000..d9ce72b
--- /dev/null
+++ b/tests/gcode/linuxcnc_fractional_linenumbers.ngc
@@ -0,0 +1,4 @@
+S300
+N1234 S600
+N4567.789 S1200
+M2