diff --git a/src/sfizz/Defaults.cpp b/src/sfizz/Defaults.cpp
index 40ce37c7..d70f3f83 100644
--- a/src/sfizz/Defaults.cpp
+++ b/src/sfizz/Defaults.cpp
@@ -41,7 +41,7 @@ FloatSpec oscillatorDetuneMod { 0.0f, {-12000.0f, 12000.0f}, kPermissiveBounds }
 FloatSpec oscillatorModDepth { 0.0f, {0.0f, 10000.0f}, kNormalizePercent|kPermissiveBounds };
 FloatSpec oscillatorModDepthMod { 0.0f, {0.0f, 10000.0f}, kNormalizePercent|kPermissiveBounds };
 Int32Spec oscillatorQuality { 1, {0, 3}, 0 };
-UInt32Spec group { 0, {0, uint32_t_max}, 0 };
+Int64Spec group { 0, {-int32_t_max, uint32_t_max}, 0 };
 FloatSpec offTime { 6e-3f, {0.0f, 100.0f}, kPermissiveBounds };
 UInt32Spec polyphony { config::maxVoices, {0, config::maxVoices}, kEnforceBounds };
 UInt32Spec notePolyphony { config::maxVoices, {1, config::maxVoices}, kEnforceBounds };
diff --git a/src/sfizz/Defaults.h b/src/sfizz/Defaults.h
index 7d6c54fa..05fc5a37 100644
--- a/src/sfizz/Defaults.h
+++ b/src/sfizz/Defaults.h
@@ -153,7 +153,7 @@ namespace Default
     extern const OpcodeSpec<float> oscillatorModDepth;
     extern const OpcodeSpec<float> oscillatorModDepthMod;
     extern const OpcodeSpec<int32_t> oscillatorQuality;
-    extern const OpcodeSpec<uint32_t> group;
+    extern const OpcodeSpec<int64_t> group;
     extern const OpcodeSpec<float> offTime;
     extern const OpcodeSpec<uint32_t> polyphony;
     extern const OpcodeSpec<uint32_t> notePolyphony;
diff --git a/src/sfizz/FlexEnvelope.cpp b/src/sfizz/FlexEnvelope.cpp
index 3cbd4161..39a387af 100644
--- a/src/sfizz/FlexEnvelope.cpp
+++ b/src/sfizz/FlexEnvelope.cpp
@@ -95,8 +95,6 @@ void FlexEnvelope::configure(const FlexEGDescription* desc)
 void FlexEnvelope::start(unsigned triggerDelay)
 {
     Impl& impl = *impl_;
-    const FlexEGDescription& desc = *impl.desc_;
-
     impl.delayFramesLeft_ = triggerDelay;
     impl.currentFramesUntilRelease_ = absl::nullopt;
     impl.advanceToStage(0);
@@ -116,6 +114,7 @@ void FlexEnvelope::release(unsigned releaseDelay)
 
 void FlexEnvelope::cancelRelease(unsigned delay)
 {
+    UNUSED(delay);
     Impl& impl = *impl_;
     const FlexEGDescription& desc = *impl.desc_;
 
@@ -249,8 +248,6 @@ void FlexEnvelope::Impl::process(absl::Span<float> out)
 bool FlexEnvelope::Impl::advanceToStage(unsigned stageNumber)
 {
     const FlexEGDescription& desc = *desc_;
-    const MidiState& midiState = resources_->getMidiState();
-
     currentStageNumber_ = stageNumber;
 
     if (stageNumber >= desc.points.size())
diff --git a/src/sfizz/Region.h b/src/sfizz/Region.h
index fe407065..95dfec54 100644
--- a/src/sfizz/Region.h
+++ b/src/sfizz/Region.h
@@ -327,8 +327,8 @@ struct Region {
     absl::optional<int> oscillatorQuality;
 
     // Instrument settings: voice lifecycle
-    uint32_t group { Default::group }; // group
-    absl::optional<uint32_t> offBy {}; // off_by
+    int64_t group { Default::group }; // group
+    absl::optional<int64_t> offBy {}; // off_by
     OffMode offMode { Default::offMode }; // off_mode
     float offTime { Default::offTime }; // off_mode
     absl::optional<uint32_t> notePolyphony {}; // note_polyphony
diff --git a/src/sfizz/VoiceManager.cpp b/src/sfizz/VoiceManager.cpp
index 862626d7..7440f5cf 100644
--- a/src/sfizz/VoiceManager.cpp
+++ b/src/sfizz/VoiceManager.cpp
@@ -19,7 +19,7 @@ void VoiceManager::onVoiceStateChanging(NumericId<Voice> id, Voice::State state)
         const uint32_t group = region->group;
         RegionSet::removeVoiceFromHierarchy(region, voice);
         swapAndPopFirst(activeVoices_, [voice](const Voice* v) { return v == voice; });
-        ASSERT(group < polyphonyGroups_.size());
+        ASSERT(polyphonyGroups_.contains(group));
         polyphonyGroups_[group].removeVoice(voice);
     } else if (state == Voice::State::playing) {
         Voice* voice = getVoiceById(id);
@@ -27,7 +27,7 @@ void VoiceManager::onVoiceStateChanging(NumericId<Voice> id, Voice::State state)
         const uint32_t group = region->group;
         activeVoices_.push_back(voice);
         RegionSet::registerVoiceInHierarchy(region, voice);
-        ASSERT(group < polyphonyGroups_.size());
+        ASSERT(polyphonyGroups_.contains(group));
         polyphonyGroups_[group].registerVoice(voice);
     }
 }
@@ -61,8 +61,7 @@ void VoiceManager::reset()
         voice.reset();
 
     polyphonyGroups_.clear();
-    polyphonyGroups_.emplace_back();
-    polyphonyGroups_.back().setPolyphonyLimit(config::maxVoices);
+    polyphonyGroups_.emplace(0, PolyphonyGroup{});
     setStealingAlgorithm(StealingAlgorithm::Oldest);
 }
 
@@ -84,29 +83,31 @@ bool VoiceManager::playingAttackVoice(const Region* releaseRegion) noexcept
         return true;
 }
 
-void VoiceManager::ensureNumPolyphonyGroups(unsigned groupIdx) noexcept
+void VoiceManager::ensureNumPolyphonyGroups(int groupIdx) noexcept
 {
-    size_t neededSize = static_cast<size_t>(groupIdx) + 1;
-    if (polyphonyGroups_.size() < neededSize)
-        polyphonyGroups_.resize(neededSize);
+    if (!polyphonyGroups_.contains(groupIdx))
+        polyphonyGroups_.emplace(groupIdx, PolyphonyGroup{});
 }
 
-void VoiceManager::setGroupPolyphony(unsigned groupIdx, unsigned polyphony) noexcept
+void VoiceManager::setGroupPolyphony(int groupIdx, unsigned polyphony) noexcept
 {
     ensureNumPolyphonyGroups(groupIdx);
     polyphonyGroups_[groupIdx].setPolyphonyLimit(polyphony);
 }
 
 
-const PolyphonyGroup* VoiceManager::getPolyphonyGroupView(int idx) const noexcept
+const PolyphonyGroup* VoiceManager::getPolyphonyGroupView(int idx) noexcept
 {
-    return (size_t)idx < polyphonyGroups_.size() ? &polyphonyGroups_[idx] : nullptr;
+    if (!polyphonyGroups_.contains(idx))
+        return {};
+
+    return &polyphonyGroups_[idx];
 }
 
 void VoiceManager::clear()
 {
-    for (PolyphonyGroup& pg : polyphonyGroups_)
-        pg.removeAllVoices();
+    for (auto& pg : polyphonyGroups_)
+        pg.second.removeAllVoices();
     list_.clear();
     activeVoices_.clear();
 }
diff --git a/src/sfizz/VoiceManager.h b/src/sfizz/VoiceManager.h
index b4e22d4d..785f271c 100644
--- a/src/sfizz/VoiceManager.h
+++ b/src/sfizz/VoiceManager.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include "absl/container/flat_hash_map.h"
 #include "Config.h"
 #include "PolyphonyGroup.h"
 #include "Region.h"
@@ -59,7 +60,7 @@ struct VoiceManager final : public Voice::StateListener
      *
      * @param groupIdx
      */
-    void ensureNumPolyphonyGroups(unsigned groupIdx) noexcept;
+    void ensureNumPolyphonyGroups(int groupIdx) noexcept;
 
     /**
      * @brief Set the polyphony for a given group
@@ -69,7 +70,7 @@ struct VoiceManager final : public Voice::StateListener
      * @param groupIdx
      * @param polyphony
      */
-    void setGroupPolyphony(unsigned groupIdx, unsigned polyphony) noexcept;
+    void setGroupPolyphony(int groupIdx, unsigned polyphony) noexcept;
 
     /**
      * @brief Get a view into a given polyphony group
@@ -77,7 +78,7 @@ struct VoiceManager final : public Voice::StateListener
      * @param idx
      * @return const PolyphonyGroup*
      */
-    const PolyphonyGroup* getPolyphonyGroupView(int idx) const noexcept;
+    const PolyphonyGroup* getPolyphonyGroupView(int idx) noexcept;
 
     /**
      * @brief Clear all voices and polyphony groups.
@@ -138,7 +139,7 @@ private:
     std::vector<Voice*> activeVoices_;
     std::vector<Voice*> temp_;
     // These are the `group=` groups where you can off voices
-    std::vector<PolyphonyGroup> polyphonyGroups_;
+    absl::flat_hash_map<int, PolyphonyGroup> polyphonyGroups_;
     std::unique_ptr<VoiceStealer> stealer_ { absl::make_unique<OldestStealer>() };
 
     /**
diff --git a/tests/PolyphonyT.cpp b/tests/PolyphonyT.cpp
index 0a966da9..f07e6c91 100644
--- a/tests/PolyphonyT.cpp
+++ b/tests/PolyphonyT.cpp
@@ -57,7 +57,7 @@ TEST_CASE("[Polyphony] Polyphony groups")
         <group> group=4
         <region> key=62 sample=*sine
     )");
-    REQUIRE( synth.getNumPolyphonyGroups() == 5 );
+    REQUIRE( synth.getNumPolyphonyGroups() == 4 );
     REQUIRE( synth.getNumRegions() == 5 );
     REQUIRE( synth.getRegionView(0)->group == 0 );
     REQUIRE( synth.getRegionView(1)->group == 1 );
@@ -67,7 +67,7 @@ TEST_CASE("[Polyphony] Polyphony groups")
     REQUIRE( synth.getRegionView(4)->group == 4 );
     REQUIRE( synth.getPolyphonyGroupView(1)->getPolyphonyLimit() == 3 );
     REQUIRE( synth.getPolyphonyGroupView(2)->getPolyphonyLimit() == 4 );
-    REQUIRE( synth.getPolyphonyGroupView(3)->getPolyphonyLimit() == sfz::config::maxVoices );
+    REQUIRE( !synth.getPolyphonyGroupView(3) );
     REQUIRE( synth.getPolyphonyGroupView(4)->getPolyphonyLimit() == 5 );
 }
 
diff --git a/tests/RegionValuesT.cpp b/tests/RegionValuesT.cpp
index 970a259e..633c6afe 100644
--- a/tests/RegionValuesT.cpp
+++ b/tests/RegionValuesT.cpp
@@ -426,7 +426,7 @@ TEST_CASE("[Values] Group")
     synth.loadSfzString(fs::current_path() / "tests/TestFiles/value_tests.sfz", R"(
         <region> sample=kick.wav
         <region> sample=kick.wav group=5
-        <region> sample=kick.wav group=-1
+        <region> sample=kick.wav group=-2
     )");
     synth.dispatchMessage(client, 0, "/region0/group", "", nullptr);
     synth.dispatchMessage(client, 0, "/region1/group", "", nullptr);
@@ -434,7 +434,7 @@ TEST_CASE("[Values] Group")
     std::vector<std::string> expected {
         "/region0/group,h : { 0 }",
         "/region1/group,h : { 5 }",
-        "/region2/group,h : { 0 }",
+        "/region2/group,h : { -2 }",
     };
     REQUIRE(messageList == expected);
 }
@@ -448,7 +448,7 @@ TEST_CASE("[Values] Off by")
     synth.loadSfzString(fs::current_path() / "tests/TestFiles/value_tests.sfz", R"(
         <region> sample=kick.wav
         <region> sample=kick.wav off_by=5
-        <region> sample=kick.wav off_by=-1
+        <region> sample=kick.wav off_by=-2
     )");
     synth.dispatchMessage(client, 0, "/region0/off_by", "", nullptr);
     synth.dispatchMessage(client, 0, "/region1/off_by", "", nullptr);
@@ -456,7 +456,7 @@ TEST_CASE("[Values] Off by")
     std::vector<std::string> expected {
         "/region0/off_by,N : {  }",
         "/region1/off_by,h : { 5 }",
-        "/region2/off_by,N : {  }",
+        "/region2/off_by,h : { -2 }",
     };
     REQUIRE(messageList == expected);
 }
diff --git a/tests/SynthT.cpp b/tests/SynthT.cpp
index 639acefa..ad099fde 100644
--- a/tests/SynthT.cpp
+++ b/tests/SynthT.cpp
@@ -1595,6 +1595,29 @@ TEST_CASE("[Synth] Off by standard")
     REQUIRE( playingVoices.front()->getRegion()->keyRange.containsWithEnd(60) );
 }
 
+TEST_CASE("[Synth] Off by negative groups")
+{
+    sfz::Synth synth;
+    sfz::AudioBuffer<float> buffer { 2, static_cast<unsigned>(synth.getSamplesPerBlock()) };
+
+    synth.loadSfzString(fs::current_path(), R"(
+        <region> group=-1 off_by=-2 sample=*saw transpose=12 key=60
+        <region> group=-2 off_by=-1 sample=*triangle key=62
+    )");
+    synth.noteOn(0, 60, 85);
+    synth.renderBlock(buffer);
+    REQUIRE( numPlayingVoices(synth) == 1 );
+    synth.noteOn(10, 62, 85);
+    synth.renderBlock(buffer);
+    REQUIRE( numPlayingVoices(synth) == 1 );
+    auto playingVoices = getPlayingVoices(synth);
+    REQUIRE( playingVoices.front()->getRegion()->keyRange.containsWithEnd(62) );
+    synth.noteOn(10, 60, 85);
+    synth.renderBlock(buffer);
+    playingVoices = getPlayingVoices(synth);
+    REQUIRE( playingVoices.front()->getRegion()->keyRange.containsWithEnd(60) );
+}
+
 TEST_CASE("[Synth] Off by same group")
 {
     sfz::Synth synth;