diff --git a/sound_algo/data_only/matrix.scd b/sound_algo/data_only/matrix.scd
index d0610f2..d171fc1 100644
--- a/sound_algo/data_only/matrix.scd
+++ b/sound_algo/data_only/matrix.scd
@@ -124,17 +124,18 @@ File.exists(~matDir).not.if({ ("mkdir -p " ++ ~matDir.quote).systemCmd });
                 (stretch: 0.5, octave:  0, amp: 1.2)
             ][color];
             spec.notNil.if({
+                var inst = ~matInstruments[vi];
+                var instPair = inst.notNil.if({ [\instrument, inst] }, { [] });
                 Pchain(
-                    Pbind(
+                    Pbind(*([
                         \matGlow, Pfunc { |e|
                             ~matEmitTrig.(vi, (e[\amp] ? spec[\amp]).clip(0, 1));
                             0
                         },
                         \stretch, spec[\stretch],
                         \octave,  spec[\octave],
-                        \amp,     spec[\amp],
-                        \instrument, Pfunc { ~matInstruments[vi] }   // nil → base \instrument kept
-                    ),
+                        \amp,     spec[\amp]
+                    ] ++ instPair)),
                     base
                 )
             }, { base })
@@ -371,7 +372,7 @@ OSCdef(\mat_list, { |msg, time, addr|
 
 OSCdef(\mat_inst, { |msg, time, addr|
     ~toscTouch !? { ~toscTouch.(addr) };
-    ~matApplyInstrument.(msg[1].asInteger, (msg[2] ? \default).asSymbol)
+    ~matApplyInstrument.((msg[1] ? 0).asInteger, (msg[2] ? \default).asSymbol)
 }, '/matrix/instrument');
 
 OSCdef(\mat_kit, { |msg, time, addr|
diff --git a/sound_algo/data_only/test/test_matrix.scd b/sound_algo/data_only/test/test_matrix.scd
index ed32d01..3382ff1 100644
--- a/sound_algo/data_only/test/test_matrix.scd
+++ b/sound_algo/data_only/test/test_matrix.scd
@@ -18,9 +18,9 @@ var glowPat   = nil;
 ~toscTouch = { |addr| };          // stub
 
 // Define dummy base Pdefs so ~matVariation has something to capture
-Pdef(\lp_kick, Pbind(\dur, 1));
-Pdef(\lp_hats, Pbind(\dur, 0.5));
-Pdef(\lp_arp,  Pbind(\dur, 0.25));   // needed by Task-1 instrument overlay test (vi=6)
+Pdef(\lp_kick, Pbind(\instrument, \lp_kick,  \dur, 1));
+Pdef(\lp_hats, Pbind(\instrument, \lp_hat,   \dur, 0.5));
+Pdef(\lp_arp,  Pbind(\instrument, \lp_pluck, \dur, 0.25));   // needed by Task-1 instrument overlay test (vi=6)
 
 // Load the feature file (synchronous; stubs and Pdefs already in place)
 featureFile.load;
@@ -181,6 +181,16 @@ try { ~trigLog2 = ~matVariation.(\arp, 2, 6).asStream.next(()) } { |e| pass = fa
 pass = pass and: { ~trigLog2.notNil and: { ~trigLog2[\instrument] == \do_strike } };
 ~matVoices.size.do { |i| ~matInstruments[i] = nil };   // reset for later tests
 
+// REGRESSION: a nil-instrument (default) voice must still produce a sounding event
+~matInstruments[0] = nil;                          // kick = default
+~regEv = ~matVariation.(\kick, 2, 0).asStream.next(());
+pass = pass and: { ~regEv.notNil };                // NOT stream-ended
+pass = pass and: { ~regEv[\instrument] == \lp_kick };   // base instrument preserved
+~matInstruments[0] = \do_kick;                     // override
+~regEv2 = ~matVariation.(\kick, 2, 0).asStream.next(());
+pass = pass and: { ~regEv2[\instrument] == \do_kick };
+~matInstruments[0] = nil;
+
 pass.if(
     { "TEST PASS".postln },
     { "TEST FAIL".postln }