diff --git a/serial.cpp b/serial.cpp
index 375c9cf6..c29dda99 100644
--- a/serial.cpp
+++ b/serial.cpp
@@ -210,7 +210,6 @@ std::string serialize_feature(serial_feature *sf, long long wx, long long wy) {
 
 	if (sf->index != 0) {
 		serialize_ulong_long(s, sf->index);
-		serialize_ulong_long(s, sf->previndex);
 		serialize_ulong_long(s, sf->gap);
 	}
 	if (sf->label_point != 0) {
@@ -260,7 +259,6 @@ serial_feature deserialize_feature(std::string const &geoms, unsigned z, unsigne
 	deserialize_int(&cp, &sf.segment);
 
 	sf.index = 0;
-	sf.previndex = 0;
 	sf.gap = 0;
 	sf.label_point = 0;
 	sf.extent = 0;
@@ -269,7 +267,6 @@ serial_feature deserialize_feature(std::string const &geoms, unsigned z, unsigne
 
 	if (sf.layer & (1 << FLAG_INDEX)) {
 		deserialize_ulong_long(&cp, &sf.index);
-		deserialize_ulong_long(&cp, &sf.previndex);
 		deserialize_ulong_long(&cp, &sf.gap);
 	}
 	if (sf.layer & (1 << FLAG_LABEL_POINT)) {
diff --git a/serial.hpp b/serial.hpp
index 805199cd..91479a4a 100644
--- a/serial.hpp
+++ b/serial.hpp
@@ -67,8 +67,7 @@ struct serial_feature {
 
 	drawvec geometry = drawvec();
 	unsigned long long index = 0;
-	unsigned long long previndex = 0;  // filled in during z0
-	unsigned long long gap = 0;	   // filled in during z0. square of planar distance
+	unsigned long long gap = 0;  // filled in during z0. square of planar distance
 	unsigned long long label_point = 0;
 	long long extent = 0;
 
diff --git a/tile.cpp b/tile.cpp
index 46fa060c..06e99fc4 100644
--- a/tile.cpp
+++ b/tile.cpp
@@ -1047,19 +1047,19 @@ static serial_feature next_feature(decompressor *geoms, std::atomic<long long> *
 
 		(*original_features)++;
 
-		if (sf.previndex == 0) {
-			sf.previndex = previndex;
+		if (sf.gap == 0) {
+			if (sf.index != previndex) {
+				unsigned wx1, wy1;
+				decode_index(sf.index, &wx1, &wy1);
 
-			unsigned wx1, wy1;
-			decode_index(sf.index, &wx1, &wy1);
+				unsigned wx2, wy2;
+				decode_index(previndex, &wx2, &wy2);
 
-			unsigned wx2, wy2;
-			decode_index(sf.previndex, &wx2, &wy2);
+				long long dx = (long long) wx1 - wx2;
+				long long dy = (long long) wy1 - wy2;
 
-			long long dx = (long long) wx1 - wx2;
-			long long dy = (long long) wy1 - wy2;
-
-			sf.gap = dx * dx + dy * dy;
+				sf.gap = dx * dx + dy * dy;
+			}
 		}
 		previndex = sf.index;
 
@@ -1735,7 +1735,7 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
 				}
 
 				if (z <= cluster_maxzoom && cluster_distance != 0) {
-					// This still uses merge_previndex instead of sf.previndex
+					// This still uses merge_previndex instead of sf.gap
 					// because the cluster size in -K is expecting to specify
 					// distances between points that are subject to dot-dropping,
 					// rather than wanting each feature to have a consistent