diff --git a/base64_amd64.go b/base64_amd64.go
index b45b6b1..3c64912 100644
--- a/base64_amd64.go
+++ b/base64_amd64.go
@@ -40,7 +40,7 @@ func decode(enc *Encoding, dst, src []byte) (int, error) {
 
 		if remain < srcLen {
 			// decoded by SIMD
-			remain = srcLen - remain
+			remain = srcLen - remain // remain is decoded length now
 			src = src[remain:]
 			dstStart := (remain / 4) * 3
 			dst = dst[dstStart:]
diff --git a/base64_arm64.go b/base64_arm64.go
index d00fadb..185e7a7 100644
--- a/base64_arm64.go
+++ b/base64_arm64.go
@@ -14,6 +14,17 @@ var dencodeStdLut = [128]byte{
 	40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 255, 255, 255, 255,
 }
 
+var dencodeUrlLut = [128]byte{
+	255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+	255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+	255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 62, 255, 255,
+	52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255, 255, 255, 255, 255,
+	0, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
+	14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255, 255,
+	63, 255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
+	40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 255, 255, 255, 255,
+}
+
 //go:noescape
 func encodeAsm(dst, src []byte, lut *[64]byte) int
 
@@ -30,5 +41,27 @@ func encode(enc *Encoding, dst, src []byte) {
 }
 
 func decode(enc *Encoding, dst, src []byte) (int, error) {
+	srcLen := len(src)
+	if srcLen >= 64 {
+		remain := srcLen
+		if enc.lut == &encodeStdLut {
+			remain = decodeAsm(dst, src, &dencodeStdLut)
+		} else if enc.lut == &encodeURLLut {
+			remain = decodeAsm(dst, src, &dencodeUrlLut)
+		}
+
+		if remain < srcLen {
+			// decoded by SIMD
+			remain = srcLen - remain // remain is decoded length now
+			src = src[remain:]
+			dstStart := (remain / 4) * 3
+			dst = dst[dstStart:]
+			n, err := decodeGeneric(enc, dst, src)
+			if cerr, ok := err.(CorruptInputError); ok {
+				return n + dstStart, CorruptInputError(int(cerr) + remain)
+			}
+			return n + dstStart, err
+		}
+	}
 	return decodeGeneric(enc, dst, src)
 }
diff --git a/base64_arm64.s b/base64_arm64.s
index d0ae56c..4c7bfed 100644
--- a/base64_arm64.s
+++ b/base64_arm64.s
@@ -107,8 +107,6 @@ loop:
 	VORR V19.B16, V16.B16, V16.B16
 
 	// Check that all bits are zero:
-	// Do NOT use UMAXV first
-	// WORD $0x6e30aa05 // VUMAXV V16.B16, R5
 	VMOV V16.D[0], R5
 	CBNZ R5, done
 	VMOV V16.D[1], R5
diff --git a/base64_arm64_test.go b/base64_arm64_test.go
index d393f3f..aaa3514 100644
--- a/base64_arm64_test.go
+++ b/base64_arm64_test.go
@@ -31,7 +31,8 @@ func TestStdEncodeSIMD(t *testing.T) {
 
 func TestStdDecodeSIMD(t *testing.T) {
 	pairs := []testpair{
-	//	{"abcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamts"},
+		{"abcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamts"},
+		{"abcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamt="},
 		{"abcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamts"},
 	}
 	for _, p := range pairs {
@@ -48,3 +49,45 @@ func TestStdDecodeSIMD(t *testing.T) {
 		}
 	}
 }
+
+func TestUrlEncodeSIMD(t *testing.T) {
+	pairs := []testpair{
+		{"!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~", "IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-"},
+		{"!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~", "IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-"},
+	}
+	for _, p := range pairs {
+		src := []byte(p.decoded)
+		expected := []byte(p.encoded)
+		dst := make([]byte, len(expected))
+
+		ret := encodeAsm(dst, src, &StdEncoding.encode)
+		if ret != len(expected) {
+			t.Fatalf("should return %v", len(expected))
+		}
+		if !bytes.Equal(dst, expected) {
+			t.Fatalf("got %v", string(dst))
+		}
+
+	}
+}
+
+func TestUrlDecodeSIMD(t *testing.T) {
+	pairs := []testpair{
+		{"!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~", "IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-"},
+		{"abcdefghijklabcdefghijklabcdefghijklabcdefghijkl", "YWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamtsYWJjZGVmZ2hpamt="},
+		{"!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~!?$*&()'-=@~", "IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-IT8kKiYoKSctPUB-"},
+	}
+	for _, p := range pairs {
+		expected := []byte(p.decoded)
+		src := []byte(p.encoded)
+		dst := make([]byte, len(expected))
+
+		ret := decodeAsm(dst, src, &dencodeStdLut)
+		if ret == len(src) {
+			t.Fatal("should return decode")
+		}
+		if !bytes.Equal(dst, expected) {
+			t.Fatalf("got %x, expected %x", dst, expected)
+		}
+	}
+}