diff --git a/internal/checker/checker.go b/internal/checker/checker.go
index 6ca4a88e3b9..6f93b4f0852 100644
--- a/internal/checker/checker.go
+++ b/internal/checker/checker.go
@@ -2,6 +2,7 @@ package checker
 
 import (
 	"context"
+	"encoding/binary"
 	"fmt"
 	"iter"
 	"maps"
@@ -17352,30 +17353,6 @@ func (c *Checker) isThislessInterface(symbol *ast.Symbol) bool {
 	return true
 }
 
-func hashWrite32[T ~int32 | ~uint32](h *xxh3.Hasher, value T) {
-	v := uint32(value)
-	_, _ = h.Write([]byte{
-		byte(v),
-		byte(v >> 8),
-		byte(v >> 16),
-		byte(v >> 24),
-	})
-}
-
-func hashWrite64[T ~int | ~uint | ~int64 | ~uint64](h *xxh3.Hasher, value T) {
-	v := uint64(value)
-	_, _ = h.Write([]byte{
-		byte(v),
-		byte(v >> 8),
-		byte(v >> 16),
-		byte(v >> 24),
-		byte(v >> 32),
-		byte(v >> 40),
-		byte(v >> 48),
-		byte(v >> 56),
-	})
-}
-
 type CacheHashKey xxh3.Uint128
 
 func (k CacheHashKey) IsZero() bool {
@@ -17383,31 +17360,70 @@ func (k CacheHashKey) IsZero() bool {
 }
 
 type keyBuilder struct {
-	h xxh3.Hasher
+	inlineLength   int
+	overflowBuffer []byte
+	inlineBuffer   [192]byte
 }
 
 func (b *keyBuilder) hash() CacheHashKey {
-	return CacheHashKey(b.h.Sum128())
+	if b.overflowBuffer == nil {
+		return CacheHashKey(xxh3.Hash128(b.inlineBuffer[:b.inlineLength]))
+	}
+	return CacheHashKey(xxh3.Hash128(append(b.overflowBuffer, b.inlineBuffer[:b.inlineLength]...)))
+}
+
+// spill moves the buffered bytes onto the end of overflowBuffer, so the key's byte
+// stream stays overflowBuffer followed by inlineBuffer.
+func (b *keyBuilder) spill() {
+	b.overflowBuffer = append(b.overflowBuffer, b.inlineBuffer[:b.inlineLength]...)
+	b.inlineLength = 0
 }
 
 func (b *keyBuilder) writeByte(c byte) {
-	_, _ = b.h.Write([]byte{c})
+	if b.inlineLength == len(b.inlineBuffer) {
+		b.spill()
+	}
+	b.inlineBuffer[b.inlineLength] = c
+	b.inlineLength++
 }
 
 func (b *keyBuilder) writeString(s string) {
-	_, _ = b.h.WriteString(s)
+	if b.inlineLength+len(s) > len(b.inlineBuffer) {
+		b.spill()
+		if len(s) > len(b.inlineBuffer) {
+			b.overflowBuffer = append(b.overflowBuffer, s...)
+			return
+		}
+	}
+	b.inlineLength += copy(b.inlineBuffer[b.inlineLength:], s)
+}
+
+func (b *keyBuilder) writeUint32(v uint32) {
+	if b.inlineLength+4 > len(b.inlineBuffer) {
+		b.spill()
+	}
+	binary.LittleEndian.PutUint32(b.inlineBuffer[b.inlineLength:], v)
+	b.inlineLength += 4
+}
+
+func (b *keyBuilder) writeUint64(v uint64) {
+	if b.inlineLength+8 > len(b.inlineBuffer) {
+		b.spill()
+	}
+	binary.LittleEndian.PutUint64(b.inlineBuffer[b.inlineLength:], v)
+	b.inlineLength += 8
 }
 
 func (b *keyBuilder) writeInt(value int) {
-	hashWrite64(&b.h, value)
+	b.writeUint64(uint64(value))
 }
 
 func (b *keyBuilder) writeSymbol(s *ast.Symbol) {
-	hashWrite64(&b.h, ast.GetSymbolId(s))
+	b.writeUint64(uint64(ast.GetSymbolId(s)))
 }
 
 func (b *keyBuilder) writeType(t *Type) {
-	hashWrite32(&b.h, t.id)
+	b.writeUint32(uint32(t.id))
 }
 
 func (b *keyBuilder) writeTypes(types []*Type) {
@@ -17463,7 +17479,7 @@ func (b *keyBuilder) writeGenericTypeReferences(source *Type, target *Type, igno
 }
 
 func (b *keyBuilder) writeNodeId(id ast.NodeId) {
-	hashWrite64(&b.h, id)
+	b.writeUint64(uint64(id))
 }
 
 func (b *keyBuilder) writeNode(node *ast.Node) {
@@ -17560,7 +17576,7 @@ func getIndexedAccessKey(objectType *Type, indexType *Type, accessFlags AccessFl
 	var b keyBuilder
 	b.writeType(objectType)
 	b.writeType(indexType)
-	hashWrite32(&b.h, accessFlags)
+	b.writeUint32(uint32(accessFlags))
 	b.writeAlias(alias)
 	return b.hash()
 }
@@ -17603,7 +17619,7 @@ func getRelationKey(source *Type, target *Type, intersectionState IntersectionSt
 		b.writeType(source)
 		b.writeType(target)
 	}
-	hashWrite32(&b.h, intersectionState)
+	b.writeUint32(uint32(intersectionState))
 	return b.hash(), constrained
 }