diff --git a/compiler.go b/compiler.go
index 07270501..11ca3cac 100644
--- a/compiler.go
+++ b/compiler.go
@@ -1523,6 +1523,28 @@ func (c *Compiler) parseBuiltin(frame *Frame, args []ssa.Value, callName string)
 		default:
 			return llvm.Value{}, errors.New("todo: cap: unknown type")
 		}
+	case "copy":
+		dst, err := c.parseExpr(frame, args[0])
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		src, err := c.parseExpr(frame, args[1])
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		if _, ok := args[1].Type().(*types.Basic); ok {
+			return llvm.Value{}, errors.New("todo: copy: string to []byte")
+		}
+		dstLen := c.builder.CreateExtractValue(dst, 1, "copy.dstLen")
+		srcLen := c.builder.CreateExtractValue(src, 1, "copy.srcLen")
+		dstBuf := c.builder.CreateExtractValue(dst, 0, "copy.dstArray")
+		srcBuf := c.builder.CreateExtractValue(src, 0, "copy.srcArray")
+		elemType := dstBuf.Type().ElementType()
+		dstBuf = c.builder.CreateBitCast(dstBuf, c.i8ptrType, "copy.dstPtr")
+		srcBuf = c.builder.CreateBitCast(srcBuf, c.i8ptrType, "copy.srcPtr")
+		elemSize := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(elemType), false)
+		sliceCopy := c.mod.NamedFunction("runtime.sliceCopy")
+		return c.builder.CreateCall(sliceCopy, []llvm.Value{dstBuf, srcBuf, dstLen, srcLen, elemSize}, "copy.n"), nil
 	case "len":
 		value, err := c.parseExpr(frame, args[0])
 		if err != nil {
diff --git a/src/examples/test/test.go b/src/examples/test/test.go
index ec899559..537bc77d 100644
--- a/src/examples/test/test.go
+++ b/src/examples/test/test.go
@@ -37,11 +37,13 @@ func main() {
 	// slice
 	l := 5
 	foo := []int{1, 2, 4, 5}
-	bar := make([]byte, l-2, l)
+	bar := make([]int, l-2, l)
 	println("len/cap foo:", len(foo), cap(foo))
 	println("len/cap bar:", len(bar), cap(bar))
 	println("foo[3]:", foo[3])
 	println("sum foo:", sum(foo))
+	println("copy foo -> bar:", copy(bar, foo))
+	println("sum bar:", sum(bar))
 
 	// interfaces, pointers
 	thing := &Thing{"foo"}
diff --git a/src/runtime/runtime.go b/src/runtime/runtime.go
index e7c7f23b..c6e892d6 100644
--- a/src/runtime/runtime.go
+++ b/src/runtime/runtime.go
@@ -63,6 +63,25 @@ func memcpy(dst, src unsafe.Pointer, size uintptr) {
 	}
 }
 
+// Copy size bytes from src to dst. The memory areas may overlap and will do the
+// correct thing.
+func memmove(dst, src unsafe.Pointer, size uintptr) {
+	if uintptr(dst) < uintptr(src) {
+		// Copy forwards.
+		memcpy(dst, src, size)
+		return
+	}
+	// Copy backwards.
+	i := size
+	for {
+		i--
+		*(*uint8)(unsafe.Pointer(uintptr(dst) + i)) = *(*uint8)(unsafe.Pointer(uintptr(src) + i))
+		if i == 0 {
+			break
+		}
+	}
+}
+
 // Set the given number of bytes to zero.
 func memzero(ptr unsafe.Pointer, size uintptr) {
 	for i := uintptr(0); i < size; i++ {
@@ -81,3 +100,14 @@ func memequal(x, y unsafe.Pointer, n uintptr) bool {
 	}
 	return true
 }
+
+// Builtin copy(dst, src) function: copy bytes from dst to src.
+func sliceCopy(dst, src unsafe.Pointer, dstLen, srcLen lenType, elemSize uintptr) lenType {
+	// n = min(srcLen, dstLen)
+	n := srcLen
+	if n > dstLen {
+		n = dstLen
+	}
+	memmove(dst, src, uintptr(n)*elemSize)
+	return n
+}