diff --git a/bits_amd64.go b/bits_amd64.go
index 2d95b40..5bd6ac7 100644
--- a/bits_amd64.go
+++ b/bits_amd64.go
@@ -31,12 +31,12 @@ const (
 type bitset uint16
 
 func metaMatchH2(m *metadata, h h2) bitset {
-	b := simd.MatchMetadata((*[16]int8)(m), int8(h))
+	b := simd.MatchMetadata((*[groupSize]uint8)(m), uint8(h))
 	return bitset(b)
 }
 
 func metaMatchEmpty(m *metadata) bitset {
-	b := simd.MatchMetadata((*[16]int8)(m), empty)
+	b := simd.MatchMetadata((*[groupSize]uint8)(m), empty)
 	return bitset(b)
 }
 
diff --git a/bits_test.go b/bits_test.go
index b928d55..291d4ae 100644
--- a/bits_test.go
+++ b/bits_test.go
@@ -26,7 +26,7 @@ import (
 func TestMatchMetadata(t *testing.T) {
 	var meta metadata
 	for i := range meta {
-		meta[i] = int8(i)
+		meta[i] = uint8(i)
 	}
 	t.Run("metaMatchH2", func(t *testing.T) {
 		for _, x := range meta {
@@ -43,7 +43,7 @@ func TestMatchMetadata(t *testing.T) {
 			mask = metaMatchEmpty(&meta)
 			assert.NotZero(t, mask)
 			assert.Equal(t, uint32(i), nextMatch(&mask))
-			meta[i] = int8(i)
+			meta[i] = uint8(i)
 		}
 	})
 	t.Run("nextMatch", func(t *testing.T) {
@@ -54,7 +54,7 @@ func TestMatchMetadata(t *testing.T) {
 			assert.Equal(t, uint32(i), nextMatch(&mask))
 		}
 		for i := 0; i < len(meta); i += 2 {
-			meta[i] = int8(42)
+			meta[i] = uint8(42)
 		}
 		mask = metaMatchH2(&meta, h2(42))
 		for i := 0; i < len(meta); i += 2 {
@@ -66,7 +66,7 @@ func TestMatchMetadata(t *testing.T) {
 func BenchmarkMatchMetadata(b *testing.B) {
 	var meta metadata
 	for i := range meta {
-		meta[i] = int8(i)
+		meta[i] = uint8(i)
 	}
 	var mask bitset
 	for i := 0; i < b.N; i++ {
@@ -90,14 +90,13 @@ func nextPow2(x uint32) uint32 {
 }
 
 func TestConstants(t *testing.T) {
-	c1, c2 := empty, tombstone
-	assert.Equal(t, byte(0b1000_0000), byte(c1))
-	assert.Equal(t, byte(0b1000_0000), reinterpretCast(c1))
-	assert.Equal(t, byte(0b1111_1110), byte(c2))
-	assert.Equal(t, byte(0b1111_1110), reinterpretCast(c2))
+	assert.Equal(t, byte(0b1000_0000), empty)
+	assert.Equal(t, byte(0b1000_0000), reinterpretCast(empty))
+	assert.Equal(t, byte(0b1111_1110), tombstone)
+	assert.Equal(t, byte(0b1111_1110), reinterpretCast(tombstone))
 }
 
-func reinterpretCast(i int8) byte {
+func reinterpretCast(i uint8) byte {
 	return *(*byte)(unsafe.Pointer(&i))
 }
 
diff --git a/map.go b/map.go
index d2b188e..4ed9078 100644
--- a/map.go
+++ b/map.go
@@ -36,7 +36,7 @@ type Map[K comparable, V any] struct {
 // metadata is the h2 metadata array for a group.
 // find operations first probe the controls bytes
 // to filter candidates before matching keys
-type metadata [groupSize]int8
+type metadata [groupSize]uint8
 
 // group is a group of 16 key-value pairs
 type group[K comparable, V any] struct {
@@ -47,15 +47,15 @@ type group[K comparable, V any] struct {
 const (
 	h1Mask    uint64 = 0xffff_ffff_ffff_ff80
 	h2Mask    uint64 = 0x0000_0000_0000_007f
-	empty     int8   = -128 // 0b1000_0000
-	tombstone int8   = -2   // 0b1111_1110
+	empty     uint8  = 0b1000_0000
+	tombstone uint8  = 0b1111_1110
 )
 
 // h1 is a 57 bit hash prefix
 type h1 uint64
 
 // h2 is a 7 bit hash suffix
-type h2 int8
+type h2 uint8
 
 // NewMap constructs a Map.
 func NewMap[K comparable, V any](sz uint32) (m *Map[K, V]) {
@@ -150,7 +150,7 @@ func (m *Map[K, V]) Put(key K, value V) {
 			s := nextMatch(&matches)
 			m.groups[g].keys[s] = key
 			m.groups[g].values[s] = value
-			m.ctrl[g][s] = int8(lo)
+			m.ctrl[g][s] = uint8(lo)
 			m.resident++
 			return
 		}
diff --git a/simd/match.s b/simd/match.s
index 0e95b87..5aa2e13 100644
--- a/simd/match.s
+++ b/simd/match.s
@@ -4,11 +4,11 @@
 
 #include "textflag.h"
 
-// func MatchMetadata(metadata *[16]int8, hash int8) uint16
+// func MatchMetadata(metadata *[16]uint8, hash uint8) uint16
 // Requires: SSE2, SSSE3
 TEXT ·MatchMetadata(SB), NOSPLIT, $0-18
 	MOVQ     metadata+0(FP), AX
-	MOVBLSX  hash+8(FP), CX
+	MOVBLZX  hash+8(FP), CX
 	MOVD     CX, X0
 	PXOR     X1, X1
 	PSHUFB   X1, X0
diff --git a/simd/match_amd64.go b/simd/match_amd64.go
index 6667d93..ea93a14 100644
--- a/simd/match_amd64.go
+++ b/simd/match_amd64.go
@@ -6,4 +6,4 @@ package simd
 
 // MatchMetadata performs a 16-way probe of |metadata| using SSE instructions
 // nb: |metadata| must be an aligned pointer
-func MatchMetadata(metadata *[16]int8, hash int8) uint16
+func MatchMetadata(metadata *[16]uint8, hash uint8) uint16
diff --git a/simd/src/asm.go b/simd/src/asm.go
index 784b184..13ecf45 100644
--- a/simd/src/asm.go
+++ b/simd/src/asm.go
@@ -23,7 +23,7 @@ import (
 func main() {
 	ConstraintExpr("amd64")
 
-	TEXT("MatchMetadata", NOSPLIT, "func(metadata *[16]int8, hash int8) uint16")
+	TEXT("MatchMetadata", NOSPLIT, "func(metadata *[16]uint8, hash uint8) uint16")
 	Doc("MatchMetadata performs a 16-way probe of |metadata| using SSE instructions",
 		"nb: |metadata| must be an aligned pointer")
 	m := Mem{Base: Load(Param("metadata"), GP64())}