diff --git a/main.cpp b/main.cpp
index b419f997..7d38cd81 100644
--- a/main.cpp
+++ b/main.cpp
@@ -3098,6 +3098,7 @@ int main(int argc, char **argv) {
 		{"force-feature-limit", no_argument, &prevent[P_DYNAMIC_DROP], 1},
 		{"cluster-densest-as-needed", no_argument, &additional[A_CLUSTER_DENSEST_AS_NEEDED], 1},
 		{"keep-point-cluster-position", no_argument, &additional[A_KEEP_POINT_CLUSTER_POSITION], 1},
+		{"distinguish-duplicates", no_argument, &additional[A_DISTINGUISH_DUPLICATES], 1},
 
 		{"Dropping tightly overlapping features", 0, 0, 0},
 		{"gamma", required_argument, 0, 'g'},
diff --git a/options.hpp b/options.hpp
index 1ca5be35..83ffc2c6 100644
--- a/options.hpp
+++ b/options.hpp
@@ -29,6 +29,7 @@
 #define A_VISVALINGAM ((int) 'v')
 #define A_DETECT_WRAPAROUND ((int) 'w')
 #define A_KEEP_POINT_CLUSTER_POSITION ((int) 'a')
+#define A_DISTINGUISH_DUPLICATES ((int) 'u')
 
 #define P_TILE_COMPRESSION ((int) 'C')
 #define P_DUPLICATION ((int) 'D')
diff --git a/serial.cpp b/serial.cpp
index c1c6cf13..2aaa2d7c 100644
--- a/serial.cpp
+++ b/serial.cpp
@@ -732,7 +732,7 @@ int serialize_feature(struct serialization_state *sst, serial_feature &sf, std::
 		}
 	}
 
-	if (true || additional[A_DROP_DENSEST_AS_NEEDED] ||
+	if (additional[A_DROP_DENSEST_AS_NEEDED] ||
 	    additional[A_COALESCE_DENSEST_AS_NEEDED] ||
 	    additional[A_CLUSTER_DENSEST_AS_NEEDED] ||
 	    additional[A_CALCULATE_FEATURE_DENSITY] ||
@@ -743,6 +743,7 @@ int serialize_feature(struct serialization_state *sst, serial_feature &sf, std::
 	    prevent[P_DYNAMIC_DROP] ||
 	    additional[A_INCREASE_GAMMA_AS_NEEDED] ||
 	    additional[A_GENERATE_POLYGON_LABEL_POINTS] ||
+	    additional[A_DISTINGUISH_DUPLICATES] ||
 	    sst->uses_gamma ||
 	    retain_points_multiplier > 1 ||
 	    preserve_multiplier_density_threshold > 0 ||
diff --git a/tile.cpp b/tile.cpp
index ae5740c8..22ef2eb2 100644
--- a/tile.cpp
+++ b/tile.cpp
@@ -1088,7 +1088,7 @@ static serial_feature next_feature(decompressor *geoms, std::atomic<long long> *
 			}
 
 			s.resize(len);
-			if (fread((void *) s.c_str(), 1, len, next_feature_state.deferrals[next_feature_state.which_deferral]) != len) {
+			if (fread((void *) s.c_str(), 1, len, next_feature_state.deferrals[next_feature_state.which_deferral]) != (size_t) len) {
 				fprintf(stderr, "short read in deferred deserialization: %s\n", strerror(errno));
 				exit(EXIT_READ);
 			}
@@ -1123,7 +1123,7 @@ static serial_feature next_feature(decompressor *geoms, std::atomic<long long> *
 		sf = deserialize_feature(s, z, tx, ty, initial_x, initial_y);
 		sf.stringpool = global_stringpool + pool_off[sf.segment];
 
-		if (!next_feature_state.doing_deferrals && sf.index == next_feature_state.previndex) {
+		if (!next_feature_state.doing_deferrals && additional[A_DISTINGUISH_DUPLICATES] && sf.index == next_feature_state.previndex) {
 			if (next_feature_state.which_deferral >= next_feature_state.deferrals.size()) {
 				std::string tmpname = "/tmp/XXXXXXXXXX";
 				int fd = mkstemp((char *) tmpname.c_str());