diff --git a/src/dsp/argb_sse2.c b/src/dsp/argb_sse2.c
index 5009c5f3..fcb94a1b 100644
--- a/src/dsp/argb_sse2.c
+++ b/src/dsp/argb_sse2.c
@@ -27,14 +27,14 @@ static void PackARGB(const uint8_t* a, const uint8_t* r, const uint8_t* g,
                      const uint8_t* b, int len, uint32_t* out) {
   if (g == r + 1) {  // RGBA input order. Need to swap R and B.
     int i = 0;
-    const int len4 = len & ~3;
-    const __m128i mask = _mm_set1_epi32(0x00ff00ffu);
+    const int len_max = len & ~3;  // max length processed in main loop
+    const __m128i red_blue_mask = _mm_set1_epi32(0x00ff00ffu);
     assert(b == r + 2);
     assert(a == r + 3);
-    for (; i < len4; i += 4) {
+    for (; i < len_max; i += 4) {
       const __m128i A = _mm_loadu_si128((__m128i*)(r + 4 * i));
-      const __m128i B = _mm_and_si128(A, mask);     // R 0 B 0
-      const __m128i C = _mm_andnot_si128(mask, A);  // 0 G 0 A
+      const __m128i B = _mm_and_si128(A, red_blue_mask);     // R 0 B 0
+      const __m128i C = _mm_andnot_si128(red_blue_mask, A);  // 0 G 0 A
       const __m128i D = _mm_shufflelo_epi16(B, _MM_SHUFFLE(2, 3, 0, 1));
       const __m128i E = _mm_shufflehi_epi16(D, _MM_SHUFFLE(2, 3, 0, 1));
       const __m128i F = _mm_or_si128(E, C);
diff --git a/src/dsp/dsp.h b/src/dsp/dsp.h
index f86130b4..651f6a3c 100644
--- a/src/dsp/dsp.h
+++ b/src/dsp/dsp.h
@@ -341,6 +341,7 @@ WEBP_TSAN_IGNORE_FUNCTION void WebPInitAlphaProcessing(void);
 extern void (*VP8PackARGB)(const uint8_t* a, const uint8_t* r,
                            const uint8_t* g, const uint8_t* b, int len,
                            uint32_t* out);
+
 // RGB packing function. 'step' can be 3 or 4. r/g/b input is rgb or bgr order.
 extern void (*VP8PackRGB)(const uint8_t* r, const uint8_t* g, const uint8_t* b,
                           int len, int step, uint32_t* out);