diff --git a/main.c b/main.c
index 863116e..df996e7 100644
--- a/main.c
+++ b/main.c
@@ -6,7 +6,7 @@
 #include "mmpriv.h"
 #include "getopt.h"
 
-#define MM_VERSION "2.6-r623"
+#define MM_VERSION "2.6-r625-dirty"
 
 #ifdef __linux__
 #include <sys/resource.h>
diff --git a/sketch.c b/sketch.c
index 5453a92..7fc5352 100644
--- a/sketch.c
+++ b/sketch.c
@@ -113,26 +113,26 @@ void mm_sketch(void *km, const char *str, int len, int w, int k, uint32_t rid, i
 			}
 		} else l = 0, tq.count = tq.front = 0, kmer_span = 0;
 		buf[buf_pos] = info; // need to do this here as appropriate buf_pos and buf[buf_pos] are needed below
-		if (l == w + k - 1) { // special case for the first window - because identical k-mers are not stored yet
+		if (l == w + k - 1 && min.x != UINT64_MAX) { // special case for the first window - because identical k-mers are not stored yet
 			for (j = buf_pos + 1; j < w; ++j)
-				if (min.x == buf[j].x && buf[j].y != min.y && buf[j].y != UINT64_MAX) kv_push(mm128_t, km, *p, buf[j]);
+				if (min.x == buf[j].x && buf[j].y != min.y) kv_push(mm128_t, km, *p, buf[j]);
 			for (j = 0; j < buf_pos; ++j)
-				if (min.x == buf[j].x && buf[j].y != min.y && buf[j].y != UINT64_MAX) kv_push(mm128_t, km, *p, buf[j]);
+				if (min.x == buf[j].x && buf[j].y != min.y) kv_push(mm128_t, km, *p, buf[j]);
 		}
 		if (info.x <= min.x) { // a new minimum; then write the old min
-			if (l >= w + k && min.y != UINT64_MAX) kv_push(mm128_t, km, *p, min);
+			if (l >= w + k && min.x != UINT64_MAX) kv_push(mm128_t, km, *p, min);
 			min = info, min_pos = buf_pos;
 		} else if (buf_pos == min_pos) { // old min has moved outside the window
-			if (l >= w + k - 1) kv_push(mm128_t, km, *p, min);
+			if (l >= w + k - 1 && min.x != UINT64_MAX) kv_push(mm128_t, km, *p, min);
 			for (j = buf_pos + 1, min.x = UINT64_MAX; j < w; ++j) // the two loops are necessary when there are identical k-mers
 				if (min.x >= buf[j].x) min = buf[j], min_pos = j; // >= is important s.t. min is always the closest k-mer
 			for (j = 0; j <= buf_pos; ++j)
 				if (min.x >= buf[j].x) min = buf[j], min_pos = j;
-			if (l >= w + k - 1) { // write identical k-mers
+			if (l >= w + k - 1 && min.x != UINT64_MAX) { // write identical k-mers
 				for (j = buf_pos + 1; j < w; ++j) // these two loops make sure the output is sorted
-					if (min.x == buf[j].x && min.y != buf[j].y && buf[j].y != UINT64_MAX) kv_push(mm128_t, km, *p, buf[j]);
+					if (min.x == buf[j].x && min.y != buf[j].y) kv_push(mm128_t, km, *p, buf[j]);
 				for (j = 0; j <= buf_pos; ++j)
-					if (min.x == buf[j].x && min.y != buf[j].y && buf[j].y != UINT64_MAX) kv_push(mm128_t, km, *p, buf[j]);
+					if (min.x == buf[j].x && min.y != buf[j].y) kv_push(mm128_t, km, *p, buf[j]);
 			}
 		}
 		if (++buf_pos == w) buf_pos = 0;