diff --git a/src/kaleidoscope/MatrixAddr.h b/src/kaleidoscope/MatrixAddr.h
index 350190fd..f5aa07c7 100644
--- a/src/kaleidoscope/MatrixAddr.h
+++ b/src/kaleidoscope/MatrixAddr.h
@@ -47,7 +47,7 @@ class MatrixAddr {
   constexpr MatrixAddr(uint8_t row, uint8_t col)
     : offset_(row * cols + col) {}
 
-  constexpr MatrixAddr(uint8_t offset)
+  explicit constexpr MatrixAddr(uint8_t offset)
     : offset_(offset) {}
 
   // Rely on the default copy and move constructor.
@@ -57,8 +57,8 @@ class MatrixAddr {
   //       ridiculously bad assembler code for each copy construction,
   //       that would bloat the default firmware by 1K of PROGMEM!
   //
-  constexpr MatrixAddr(const ThisType &other) = default;
-  constexpr MatrixAddr(ThisType &&other) = default;
+  explicit constexpr MatrixAddr(const ThisType &other) = default;
+  explicit constexpr MatrixAddr(ThisType &&other) = default;
   //constexpr MatrixAddr(const ThisType &other) : offset_(other.offset_) {}
   //constexpr MatrixAddr(ThisType &&other) : offset_(other.offset_) {}
 
@@ -66,8 +66,7 @@ class MatrixAddr {
   ThisType &operator=(ThisType &&) = default;
 
   template<typename MatrixAddr__>
-  explicit
-  constexpr MatrixAddr(const MatrixAddr__ &other)
+  explicit constexpr MatrixAddr(const MatrixAddr__ &other)
     : MatrixAddr(other.row(), other.col()) {
     static_assert(MatrixAddr__::rows <= ThisType::rows,
                   "Matrix type conversion failed. Source type must not have greater row size than target type");
diff --git a/src/kaleidoscope/bitfields.h b/src/kaleidoscope/bitfields.h
index 3a59c854..52621143 100644
--- a/src/kaleidoscope/bitfields.h
+++ b/src/kaleidoscope/bitfields.h
@@ -113,7 +113,7 @@ class Bitfield : public internal::_BaseBitfield {
   static constexpr size_t n_bytes_ = nBytesForBits(BitCount__);
 
   template<typename ... Bits__>
-  constexpr Bitfield(Bits__...bits) : bits_(bits...) {
+  explicit constexpr Bitfield(Bits__...bits) : bits_(bits...) {
     static_assert(sizeof...(Bits__) == n_bits_,
                   "Invalid number of bits supplied to Bitfield<BitCount__> constructor. \n"
                   "Compare the number of bits supplied with the provided template \n"
diff --git a/src/kaleidoscope/device/dygma/raise/Hand.h b/src/kaleidoscope/device/dygma/raise/Hand.h
index 57c6ec1d..95791f68 100644
--- a/src/kaleidoscope/device/dygma/raise/Hand.h
+++ b/src/kaleidoscope/device/dygma/raise/Hand.h
@@ -56,7 +56,7 @@ typedef union {
 
 class Hand {
  public:
-  Hand(byte ad01) : ad01_(ad01), twi_(i2c_addr_base_ | ad01) {}
+  explicit Hand(byte ad01) : ad01_(ad01), twi_(i2c_addr_base_ | ad01) {}
 
   int readVersion();
   int readSLEDVersion();
diff --git a/src/kaleidoscope/device/dygma/raise/TWI.h b/src/kaleidoscope/device/dygma/raise/TWI.h
index 75298b21..ba191b09 100644
--- a/src/kaleidoscope/device/dygma/raise/TWI.h
+++ b/src/kaleidoscope/device/dygma/raise/TWI.h
@@ -27,7 +27,7 @@ namespace raise {
 
 class TWI {
  public:
-  TWI(int addr) : addr_(addr), crc_errors_(0) {}
+  explicit TWI(int addr) : addr_(addr), crc_errors_(0) {}
 
   uint8_t writeTo(uint8_t *data, size_t length);
   uint8_t readFrom(uint8_t* data, size_t length);
diff --git a/src/kaleidoscope/driver/led/Base.h b/src/kaleidoscope/driver/led/Base.h
index dedec421..d2d727bf 100644
--- a/src/kaleidoscope/driver/led/Base.h
+++ b/src/kaleidoscope/driver/led/Base.h
@@ -75,7 +75,7 @@ class Base {
     uint8_t offset_;
    public:
     LEDRangeIterator() : offset_(0) {}
-    LEDRangeIterator(uint8_t offset) : offset_(offset) {}
+    explicit LEDRangeIterator(uint8_t offset) : offset_(offset) {}
 
     typedef LEDRangeIterator ThisType;
 
diff --git a/src/kaleidoscope/key_defs.h b/src/kaleidoscope/key_defs.h
index cca19bf3..8a7de806 100644
--- a/src/kaleidoscope/key_defs.h
+++ b/src/kaleidoscope/key_defs.h
@@ -36,7 +36,7 @@ class Key {
 
   Key() = default;
 
-  constexpr Key(uint16_t raw)
+  explicit constexpr Key(uint16_t raw)
     : Key{(uint8_t)(raw & 0x00FF), (uint8_t)(raw >> 8)}
   {}
 
@@ -140,7 +140,7 @@ class Key {
 
     DataProxy() = default;
 
-    constexpr DataProxy(uint8_t value) : value_{value} {}
+    explicit constexpr DataProxy(uint8_t value) : value_{value} {}
 
     DEPRECATED(DIRECT_KEY_MEMBER_ACCESS)
     DataProxy &operator=(uint8_t value) {
diff --git a/src/kaleidoscope/plugin/Colormap.h b/src/kaleidoscope/plugin/Colormap.h
index 0389792b..bef68994 100644
--- a/src/kaleidoscope/plugin/Colormap.h
+++ b/src/kaleidoscope/plugin/Colormap.h
@@ -42,7 +42,7 @@ class ColormapEffect : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const ColormapEffect *parent) : parent_(parent) {}
+    explicit TransientLEDMode(const ColormapEffect *parent) : parent_(parent) {}
 
    protected:
 
diff --git a/src/kaleidoscope/plugin/Heatmap.h b/src/kaleidoscope/plugin/Heatmap.h
index 6a27bc48..53774b97 100644
--- a/src/kaleidoscope/plugin/Heatmap.h
+++ b/src/kaleidoscope/plugin/Heatmap.h
@@ -45,7 +45,7 @@ class Heatmap : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const Heatmap *parent);
+    explicit TransientLEDMode(const Heatmap *parent);
 
     void resetMap();
     EventHandlerResult onKeyswitchEvent(Key &mapped_key, KeyAddr key_addr, uint8_t key_state);
diff --git a/src/kaleidoscope/plugin/LED-ActiveLayerColor.h b/src/kaleidoscope/plugin/LED-ActiveLayerColor.h
index a865207d..d82587ca 100644
--- a/src/kaleidoscope/plugin/LED-ActiveLayerColor.h
+++ b/src/kaleidoscope/plugin/LED-ActiveLayerColor.h
@@ -39,7 +39,7 @@ class LEDActiveLayerColorEffect : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const LEDActiveLayerColorEffect *parent);
+    explicit TransientLEDMode(const LEDActiveLayerColorEffect *parent);
 
    protected:
 
diff --git a/src/kaleidoscope/plugin/LED-AlphaSquare/Effect.h b/src/kaleidoscope/plugin/LED-AlphaSquare/Effect.h
index 73eeae77..fffe6861 100644
--- a/src/kaleidoscope/plugin/LED-AlphaSquare/Effect.h
+++ b/src/kaleidoscope/plugin/LED-AlphaSquare/Effect.h
@@ -36,7 +36,7 @@ class AlphaSquareEffect : public Plugin,
   //
   class TransientLEDMode : public LEDMode {
    public:
-    TransientLEDMode(AlphaSquareEffect *parent);
+    explicit TransientLEDMode(AlphaSquareEffect *parent);
 
    protected:
     void update(void) final;
diff --git a/src/kaleidoscope/plugin/LED-Stalker.h b/src/kaleidoscope/plugin/LED-Stalker.h
index db099e94..8da6022a 100644
--- a/src/kaleidoscope/plugin/LED-Stalker.h
+++ b/src/kaleidoscope/plugin/LED-Stalker.h
@@ -50,7 +50,7 @@ class StalkerEffect : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const StalkerEffect *parent);
+    explicit TransientLEDMode(const StalkerEffect *parent);
 
    protected:
 
diff --git a/src/kaleidoscope/plugin/LED-Wavepool.h b/src/kaleidoscope/plugin/LED-Wavepool.h
index d52b40d1..1ff8faf9 100644
--- a/src/kaleidoscope/plugin/LED-Wavepool.h
+++ b/src/kaleidoscope/plugin/LED-Wavepool.h
@@ -51,7 +51,7 @@ class WavepoolEffect : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const WavepoolEffect *parent);
+    explicit TransientLEDMode(const WavepoolEffect *parent);
 
     EventHandlerResult onKeyswitchEvent(Key &mapped_key, KeyAddr key_addr, uint8_t key_state);
 
diff --git a/src/kaleidoscope/plugin/LEDEffect-BootGreeting.h b/src/kaleidoscope/plugin/LEDEffect-BootGreeting.h
index 180d244c..6a5478d0 100644
--- a/src/kaleidoscope/plugin/LEDEffect-BootGreeting.h
+++ b/src/kaleidoscope/plugin/LEDEffect-BootGreeting.h
@@ -24,7 +24,7 @@ namespace plugin {
 class BootGreetingEffect : public kaleidoscope::Plugin {
  public:
   BootGreetingEffect(void) {}
-  BootGreetingEffect(KeyAddr key_addr);
+  explicit BootGreetingEffect(KeyAddr key_addr);
 
   static KeyAddr user_key_addr;
   static Key search_key;
diff --git a/src/kaleidoscope/plugin/LEDEffect-Breathe.h b/src/kaleidoscope/plugin/LEDEffect-Breathe.h
index ee99ef04..2f08669e 100644
--- a/src/kaleidoscope/plugin/LEDEffect-Breathe.h
+++ b/src/kaleidoscope/plugin/LEDEffect-Breathe.h
@@ -37,7 +37,7 @@ class LEDBreatheEffect : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const LEDBreatheEffect *parent)
+    explicit TransientLEDMode(const LEDBreatheEffect *parent)
       : parent_(parent) {}
 
    protected:
diff --git a/src/kaleidoscope/plugin/LEDEffect-Chase.h b/src/kaleidoscope/plugin/LEDEffect-Chase.h
index 0ccb4400..183219e5 100644
--- a/src/kaleidoscope/plugin/LEDEffect-Chase.h
+++ b/src/kaleidoscope/plugin/LEDEffect-Chase.h
@@ -47,7 +47,7 @@ class LEDChaseEffect : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const LEDChaseEffect *parent)
+    explicit TransientLEDMode(const LEDChaseEffect *parent)
       : parent_(parent), last_update_(Runtime.millisAtCycleStart()) {}
 
    protected:
diff --git a/src/kaleidoscope/plugin/LEDEffect-Rainbow.h b/src/kaleidoscope/plugin/LEDEffect-Rainbow.h
index 1d454561..fb3cb7e7 100644
--- a/src/kaleidoscope/plugin/LEDEffect-Rainbow.h
+++ b/src/kaleidoscope/plugin/LEDEffect-Rainbow.h
@@ -43,7 +43,7 @@ class LEDRainbowEffect : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const LEDRainbowEffect *parent)
+    explicit TransientLEDMode(const LEDRainbowEffect *parent)
       : parent_(parent) {}
 
     void update() final;
@@ -88,7 +88,7 @@ class LEDRainbowWaveEffect : public Plugin, public LEDModeInterface {
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const LEDRainbowWaveEffect *parent)
+    explicit TransientLEDMode(const LEDRainbowWaveEffect *parent)
       : parent_(parent) {}
 
     void update() final;
diff --git a/src/kaleidoscope/plugin/LEDEffect-SolidColor.h b/src/kaleidoscope/plugin/LEDEffect-SolidColor.h
index 64527431..a825cfa0 100644
--- a/src/kaleidoscope/plugin/LEDEffect-SolidColor.h
+++ b/src/kaleidoscope/plugin/LEDEffect-SolidColor.h
@@ -37,7 +37,7 @@ class LEDSolidColor : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const LEDSolidColor *parent)
+    explicit TransientLEDMode(const LEDSolidColor *parent)
       : parent_(parent) {}
 
    protected:
diff --git a/src/kaleidoscope/plugin/TriColor.h b/src/kaleidoscope/plugin/TriColor.h
index 83eebcf2..574ea100 100644
--- a/src/kaleidoscope/plugin/TriColor.h
+++ b/src/kaleidoscope/plugin/TriColor.h
@@ -37,7 +37,7 @@ class TriColor : public Plugin,
     // for those LED modes that require access to
     // members of their parent class. Most LED modes can do without.
     //
-    TransientLEDMode(const TriColor *parent)
+    explicit TransientLEDMode(const TriColor *parent)
       : parent_(parent) {}
 
    protected:
diff --git a/src/kaleidoscope_internal/array_like_storage.h b/src/kaleidoscope_internal/array_like_storage.h
index 10ad9222..6001126b 100644
--- a/src/kaleidoscope_internal/array_like_storage.h
+++ b/src/kaleidoscope_internal/array_like_storage.h
@@ -85,7 +85,7 @@ struct ArrayLikeStorage<StoredType__, true /* is of appropriate type */> {
 
  public:
 
-  constexpr ArrayLikeStorage(StoredType__ entry)
+  explicit constexpr ArrayLikeStorage(StoredType__ entry)
     : entry_(entry)
   {}
 
@@ -103,7 +103,7 @@ struct ArrayLikeStorage<StoredType__, false /* not of appropriate type */> {
  public:
 
   template<typename AnyType__>
-  constexpr ArrayLikeStorage(AnyType__/* non-matching entity */) {}
+  explicit constexpr ArrayLikeStorage(AnyType__/* non-matching entity */) {}
 
   static constexpr uint8_t n_entries = 0;
 
diff --git a/src/kaleidoscope_internal/sketch_exploration/keymap_exploration.h b/src/kaleidoscope_internal/sketch_exploration/keymap_exploration.h
index 494469af..34ce8d55 100644
--- a/src/kaleidoscope_internal/sketch_exploration/keymap_exploration.h
+++ b/src/kaleidoscope_internal/sketch_exploration/keymap_exploration.h
@@ -35,7 +35,7 @@ class KeymapAdaptor {
   static constexpr uint8_t n_layers = _n_layers;
   static constexpr uint8_t layer_size = _layer_size;
 
-  constexpr KeymapAdaptor(const Key(&keymap)[_n_layers][_layer_size])
+  explicit constexpr KeymapAdaptor(const Key(&keymap)[_n_layers][_layer_size])
     :  keymap_{keymap}
   {}
 
@@ -119,7 +119,7 @@ class EmptyKeymapAccumulationHelper {
 
  public:
 
-  constexpr EmptyKeymapAccumulationHelper(const _Accumulation &op)
+  explicit constexpr EmptyKeymapAccumulationHelper(const _Accumulation &op)
     :   op_{op}
   {}
 
@@ -147,7 +147,7 @@ struct NumKeysEqual {
   typedef uint8_t ResultType;
   static constexpr ResultType init_value = 0;
 
-  constexpr NumKeysEqual(Key k) : k_{k} {}
+  explicit constexpr NumKeysEqual(Key k) : k_{k} {}
 
   constexpr ResultType apply(Key test_key, ResultType r) const {
     return (test_key == k_) ? r + 1 : r;
@@ -163,7 +163,7 @@ struct HasKey {
   typedef bool ResultType;
   static constexpr ResultType init_value = false;
 
-  constexpr HasKey(Key k) : k_{k} {}
+  explicit constexpr HasKey(Key k) : k_{k} {}
 
   constexpr ResultType apply(Key test_key, ResultType r) const {
     return (test_key == k_) ? true : r;