diff --git a/attribute.cpp b/attribute.cpp
index 2a01c2b2..1b12c960 100644
--- a/attribute.cpp
+++ b/attribute.cpp
@@ -2,7 +2,9 @@
 #include <map>
 #include "attribute.hpp"
 #include "errors.hpp"
+#include "serial.hpp"
 #include "jsonpull/jsonpull.h"
+#include "milo/dtoa_milo.h"
 
 void set_attribute_accum(std::map<std::string, attribute_op> &attribute_accum, std::string name, std::string type) {
 	attribute_op t;
@@ -76,3 +78,69 @@ void set_attribute_accum(std::map<std::string, attribute_op> &attribute_accum, c
 
 	set_attribute_accum(attribute_accum, name, type);
 }
+
+void preserve_attribute(attribute_op op, std::string &key, serial_val &val, std::vector<std::string> &full_keys, std::vector<serial_val> &full_values, std::map<std::string, accum_state> &attribute_accum_state) {
+	for (size_t i = 0; i < full_keys.size(); i++) {
+		if (key == full_keys[i]) {
+			switch (op) {
+			case op_sum:
+				full_values[i].s = milo::dtoa_milo(atof(full_values[i].s.c_str()) + atof(val.s.c_str()));
+				full_values[i].type = mvt_double;
+				break;
+
+			case op_product:
+				full_values[i].s = milo::dtoa_milo(atof(full_values[i].s.c_str()) * atof(val.s.c_str()));
+				full_values[i].type = mvt_double;
+				break;
+
+			case op_max: {
+				double existing = atof(full_values[i].s.c_str());
+				double maybe = atof(val.s.c_str());
+				if (maybe > existing) {
+					full_values[i].s = val.s.c_str();
+					full_values[i].type = mvt_double;
+				}
+				break;
+			}
+
+			case op_min: {
+				double existing = atof(full_values[i].s.c_str());
+				double maybe = atof(val.s.c_str());
+				if (maybe < existing) {
+					full_values[i].s = val.s.c_str();
+					full_values[i].type = mvt_double;
+				}
+				break;
+			}
+
+			case op_mean: {
+				auto state = attribute_accum_state.find(key);
+				if (state == attribute_accum_state.end()) {
+					accum_state s;
+					s.sum = atof(full_values[i].s.c_str()) + atof(val.s.c_str());
+					s.count = 2;
+					attribute_accum_state.insert(std::pair<std::string, accum_state>(key, s));
+
+					full_values[i].s = milo::dtoa_milo(s.sum / s.count);
+				} else {
+					state->second.sum += atof(val.s.c_str());
+					state->second.count += 1;
+
+					full_values[i].s = milo::dtoa_milo(state->second.sum / state->second.count);
+				}
+				break;
+			}
+
+			case op_concat:
+				full_values[i].s += val.s;
+				full_values[i].type = mvt_string;
+				break;
+
+			case op_comma:
+				full_values[i].s += std::string(",") + val.s;
+				full_values[i].type = mvt_string;
+				break;
+			}
+		}
+	}
+}
diff --git a/attribute.hpp b/attribute.hpp
index 1dd206e0..ebc22e7f 100644
--- a/attribute.hpp
+++ b/attribute.hpp
@@ -11,7 +11,15 @@ enum attribute_op {
 	op_min,
 };
 
+struct accum_state {
+	double sum = 0;
+	double count = 0;
+};
+
+struct serial_val;
+
 void set_attribute_accum(std::map<std::string, attribute_op> &attribute_accum, std::string name, std::string type);
 void set_attribute_accum(std::map<std::string, attribute_op> &attribute_accum, const char *arg, char **argv);
+void preserve_attribute(attribute_op op, std::string &key, serial_val &val, std::vector<std::string> &full_keys, std::vector<serial_val> &full_values, std::map<std::string, accum_state> &attribute_accum_state);
 
 #endif
diff --git a/tile.cpp b/tile.cpp
index 99ab65b9..2e25a636 100644
--- a/tile.cpp
+++ b/tile.cpp
@@ -508,11 +508,6 @@ void rewrite(drawvec &geom, int z, int nextzoom, int maxzoom, long long *bbox, u
 	}
 }
 
-struct accum_state {
-	double sum = 0;
-	double count = 0;
-};
-
 struct partial {
 	std::vector<drawvec> geoms = std::vector<drawvec>();
 	std::vector<long long> keys = std::vector<long long>();
@@ -1830,7 +1825,7 @@ void add_tilestats(std::string const &layername, int z, std::vector<std::map<std
 	add_to_file_keys(fk->second.file_keys, key, attrib);
 }
 
-void preserve_attribute(attribute_op op, serial_feature &, char *stringpool, long long *pool_off, std::string &key, serial_val &val, partial &p) {
+void promote_attribute(std::string const &key, partial &p, char *stringpool, long long *pool_off) {
 	if (p.need_tilestats.count(key) == 0) {
 		p.need_tilestats.insert(key);
 	}
@@ -1853,70 +1848,6 @@ void preserve_attribute(attribute_op op, serial_feature &, char *stringpool, lon
 			break;
 		}
 	}
-
-	for (size_t i = 0; i < p.full_keys.size(); i++) {
-		if (key == p.full_keys[i]) {
-			switch (op) {
-			case op_sum:
-				p.full_values[i].s = milo::dtoa_milo(atof(p.full_values[i].s.c_str()) + atof(val.s.c_str()));
-				p.full_values[i].type = mvt_double;
-				break;
-
-			case op_product:
-				p.full_values[i].s = milo::dtoa_milo(atof(p.full_values[i].s.c_str()) * atof(val.s.c_str()));
-				p.full_values[i].type = mvt_double;
-				break;
-
-			case op_max: {
-				double existing = atof(p.full_values[i].s.c_str());
-				double maybe = atof(val.s.c_str());
-				if (maybe > existing) {
-					p.full_values[i].s = val.s.c_str();
-					p.full_values[i].type = mvt_double;
-				}
-				break;
-			}
-
-			case op_min: {
-				double existing = atof(p.full_values[i].s.c_str());
-				double maybe = atof(val.s.c_str());
-				if (maybe < existing) {
-					p.full_values[i].s = val.s.c_str();
-					p.full_values[i].type = mvt_double;
-				}
-				break;
-			}
-
-			case op_mean: {
-				auto state = p.attribute_accum_state.find(key);
-				if (state == p.attribute_accum_state.end()) {
-					accum_state s;
-					s.sum = atof(p.full_values[i].s.c_str()) + atof(val.s.c_str());
-					s.count = 2;
-					p.attribute_accum_state.insert(std::pair<std::string, accum_state>(key, s));
-
-					p.full_values[i].s = milo::dtoa_milo(s.sum / s.count);
-				} else {
-					state->second.sum += atof(val.s.c_str());
-					state->second.count += 1;
-
-					p.full_values[i].s = milo::dtoa_milo(state->second.sum / state->second.count);
-				}
-				break;
-			}
-
-			case op_concat:
-				p.full_values[i].s += val.s;
-				p.full_values[i].type = mvt_string;
-				break;
-
-			case op_comma:
-				p.full_values[i].s += std::string(",") + val.s;
-				p.full_values[i].type = mvt_string;
-				break;
-			}
-		}
-	}
 }
 
 void preserve_attributes(std::map<std::string, attribute_op> const *attribute_accum, serial_feature &sf, char *stringpool, long long *pool_off, partial &p) {
@@ -1929,7 +1860,8 @@ void preserve_attributes(std::map<std::string, attribute_op> const *attribute_ac
 
 		auto f = attribute_accum->find(key);
 		if (f != attribute_accum->end()) {
-			preserve_attribute(f->second, sf, stringpool, pool_off, key, sv, p);
+			promote_attribute(key, p, stringpool, pool_off);
+			preserve_attribute(f->second, key, sv, p.full_keys, p.full_values, p.attribute_accum_state);
 		}
 	}
 	for (size_t i = 0; i < sf.full_keys.size(); i++) {
@@ -1938,7 +1870,8 @@ void preserve_attributes(std::map<std::string, attribute_op> const *attribute_ac
 
 		auto f = attribute_accum->find(key);
 		if (f != attribute_accum->end()) {
-			preserve_attribute(f->second, sf, stringpool, pool_off, key, sv, p);
+			promote_attribute(key, p, stringpool, pool_off);
+			preserve_attribute(f->second, key, sv, p.full_keys, p.full_values, p.attribute_accum_state);
 		}
 	}
 }