diff --git a/core/src/linuxcnc_canon_bridge.cpp b/core/src/linuxcnc_canon_bridge.cpp
index 070b8f0..0b30838 100644
--- a/core/src/linuxcnc_canon_bridge.cpp
+++ b/core/src/linuxcnc_canon_bridge.cpp
@@ -211,10 +211,10 @@ void SET_FEED_RATE(double rate) {
     }
 }
 
-void SET_SPINDLE_SPEED(int, double speed) {
+void SET_SPINDLE_SPEED(int spindle, double speed) {
     trace_call("SET_SPINDLE_SPEED");
     if (active_sink) {
-        active_sink->set_spindle_speed(speed, event_line());
+        active_sink->set_spindle_speed(spindle, speed, event_line());
     }
 }
 
@@ -486,21 +486,21 @@ void SET_SPINDLE_MODE(int spindle, double mode) {
 void SPINDLE_RETRACT_TRAVERSE() {
 }
 
-void START_SPINDLE_CLOCKWISE(int, int) {
+void START_SPINDLE_CLOCKWISE(int spindle, int) {
     if (active_sink) {
-        active_sink->start_spindle(1, event_line());
+        active_sink->start_spindle(spindle, 1, event_line());
     }
 }
 
-void START_SPINDLE_COUNTERCLOCKWISE(int, int) {
+void START_SPINDLE_COUNTERCLOCKWISE(int spindle, int) {
     if (active_sink) {
-        active_sink->start_spindle(-1, event_line());
+        active_sink->start_spindle(spindle, -1, event_line());
     }
 }
 
-void STOP_SPINDLE_TURNING(int) {
+void STOP_SPINDLE_TURNING(int spindle) {
     if (active_sink) {
-        active_sink->stop_spindle(event_line());
+        active_sink->stop_spindle(spindle, event_line());
     }
 }
 
diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index 71bdbf2..ba828d7 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -210,6 +210,13 @@ CNC_SIM_RS274_VAR="$var_file" \
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_spindle_direction.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_spindle_direction.json"
+# Source basis: LinuxCNC src/emc/rs274ngc/rs274ngc_pre.cc init reads
+# [TRAJ] SPINDLES from INI_FILE_NAME, interp_execute.cc passes S-word $
+# through convert_speed(), and interp_convert.cc routes M3/M4/M5 with a $
+# selector to the selected spindle.
+INI_FILE_NAME="$multi_spindle_modes_file" CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_multi_spindle_direction.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_source_multi_spindle_direction.json"
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_spindle_modes.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_spindle_modes.json"
@@ -1789,6 +1796,24 @@ if (3, 1200, 2) not in spindle_states:
 if (4, 0, 0) not in spindle_states:
     raise SystemExit("missing source-linked M5 stopped spindle state")
 
+multi_spindle_direction = json.loads((OUTPUT_DIR / "cnc_sim_linuxcnc_source_multi_spindle_direction.json").read_text())
+multi_spindle_direction_states = [
+    (event["line"], event["tool"], event["spindle"], event["reserved"])
+    for event in multi_spindle_direction
+    if event["type"] == "set-spindle" and event["line"] in {5, 6, 7, 8}
+]
+expected_multi_spindle_direction_states = [
+    (5, 1, 1200, 0),
+    (6, 1, 1200, 1),
+    (7, 1, 1200, 2),
+    (8, 1, 0, 0),
+]
+if multi_spindle_direction_states != expected_multi_spindle_direction_states:
+    raise SystemExit(
+        "unexpected source-linked selected-spindle M3/M4/M5 states: "
+        f"{multi_spindle_direction_states!r}"
+    )
+
 spindle_modes = json.loads((OUTPUT_DIR / "cnc_sim_linuxcnc_source_spindle_modes.json").read_text())
 spindle_mode_states = [
     (event["line"], event["reserved"], event["feed"], event["tool"])
@@ -3655,6 +3680,7 @@ echo "dumped $output_dir/cnc_sim_linuxcnc_source_basic_mill.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_incremental_and_r_arc.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_rtcp_controls.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_spindle_direction.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_source_multi_spindle_direction.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_spindle_modes.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_spindle_orient.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_io_controls.json"
diff --git a/tests/gcode/linuxcnc_multi_spindle_direction.ngc b/tests/gcode/linuxcnc_multi_spindle_direction.ngc
new file mode 100644
index 0000000..0717575
--- /dev/null
+++ b/tests/gcode/linuxcnc_multi_spindle_direction.ngc
@@ -0,0 +1,9 @@
+G21 G90 G17
+(Source basis: LinuxCNC src/emc/rs274ngc/rs274ngc_pre.cc init reads [TRAJ] SPINDLES from INI_FILE_NAME.)
+(Source basis: LinuxCNC src/emc/rs274ngc/interp_execute.cc passes S-word $ through convert_speed.)
+(Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc M3/M4/M5 with $ selects a specific spindle.)
+S1200 $1
+M3 $1
+M4 $1
+M5 $1
+M30