diff --git a/ldpc_decoder.hh b/ldpc_decoder.hh
index ba84d97..0d26d27 100644
--- a/ldpc_decoder.hh
+++ b/ldpc_decoder.hh
@@ -42,15 +42,15 @@ class LDPCDecoder
 
 	typedef SIMD<int8_t, SIMD_SIZE> TYPE;
 	typedef struct { uint16_t off; uint16_t shi; } Loc;
-	typedef uint32_t wd_t;
-	static_assert(sizeof(wd_t) * 8 >= CNC, "write disable mask needs at least as many bits as max check node links");
+	typedef uint32_t wdm_t;
+	static_assert(sizeof(wdm_t) * 8 >= CNC, "write disable mask needs at least as many bits as max check node links");
 	Rotate<TYPE, D> rotate;
 
 	TYPE bnl[BNL];
 	TYPE msg[MSG];
 	TYPE pty[PTY];
 	Loc loc[LOC];
-	wd_t wd[PTY];
+	wdm_t wdm[PTY];
 	uint8_t cnc[q];
 
 	static TYPE eor(TYPE a, TYPE b)
@@ -114,6 +114,7 @@ class LDPCDecoder
 	{
 		TYPE *bl = bnl;
 		Loc *lo = loc;
+		wdm_t *wd = wdm;
 		for (int i = 0; i < q; ++i) {
 			int cnt = cnc[i];
 			int deg = cnt + 2;
@@ -122,11 +123,18 @@ class LDPCDecoder
 				TYPE min0 = vdup<TYPE>(127);
 				TYPE min1 = vdup<TYPE>(127);
 				TYPE signs = vdup<TYPE>(127);
+				bool write_conflict = false;
+				int last_offset = -1;
 
 				for (int k = 0; k < deg; ++k) {
 					TYPE tmp;
 					if (k < cnt) {
-						tmp = rotate(msg[lo[k].off], -lo[k].shi);
+						int offset = lo[k].off;
+						int shift = -lo[k].shi;
+						tmp = rotate(msg[offset], shift);
+						if (last_offset == offset)
+							write_conflict = true;
+						last_offset = offset;
 					} else if (k == cnt) {
 						tmp = pty[W*i+j];
 					} else {
@@ -170,7 +178,7 @@ class LDPCDecoder
 					TYPE tmp = vqadd(inp, out);
 
 					if (k < cnt) {
-						if (!((wd[W*i+j]>>k)&1)) {
+						if (!write_conflict || !((*wd>>k)&1)) {
 							bl[k] = out;
 							msg[lo[k].off] = rotate(tmp, lo[k].shi);
 						}
@@ -189,7 +197,7 @@ class LDPCDecoder
 						}
 					}
 				}
-				if (wd[W*i+j]) {
+				if (write_conflict) {
 					for (int first = 0, c = 1; c < cnt; ++c) {
 						if (lo[first].off != lo[c].off || c == cnt-1) {
 							int last = c - 1;
@@ -197,15 +205,16 @@ class LDPCDecoder
 								++last;
 							if (last != first) {
 								int count = last - first + 1;
-								wd_t mask = ((1 << count) - 1) << first;
-								wd_t cur = wd[W*i+j];
-								wd_t tmp = cur & mask;
-								wd_t ror = (tmp >> 1) | (tmp << (count-1));
-								wd[W*i+j] = (cur & ~mask) | (ror & mask);
+								wdm_t mask = ((1 << count) - 1) << first;
+								wdm_t cur = *wd;
+								wdm_t tmp = cur & mask;
+								wdm_t ror = (tmp >> 1) | (tmp << (count-1));
+								*wd = (cur & ~mask) | (ror & mask);
 							}
 							first = c;
 						}
 					}
+					++wd;
 				}
 				lo += cnt;
 				bl += deg;
@@ -235,6 +244,7 @@ public:
 			}
 		}
 		Loc *lo = loc;
+		wdm_t *wd = wdm;
 		for (int i = 0; i < q; ++i) {
 			int cnt = cnc[i];
 			int offset[cnt], shift[cnt];
@@ -249,10 +259,12 @@ public:
 					shift[c] = (shift[c] + 1) % M;
 				}
 				std::sort(lo, lo + cnt, [](const Loc &a, const Loc &b){ return a.off < b.off; });
-				wd[W*i+j] = 0;
+				wdm_t tmp = 0;
 				for (int c = 0; c < cnt-1; ++c)
 					if (lo[c].off == lo[c+1].off)
-						wd[W*i+j] |= 1 << c;
+						tmp |= 1 << c;
+				if (tmp)
+					*wd++ = tmp;
 				lo += cnt;
 			}
 		}