diff --git a/src/cssom/om.cpp b/src/cssom/om.cpp
index dddf824..a9139cc 100644
--- a/src/cssom/om.cpp
+++ b/src/cssom/om.cpp
@@ -283,6 +283,65 @@ std::string to_string(
 }
 } // namespace
 
+namespace {
+// Produces deterministic list of CSS rules.
+// The list is sorted by property groups and within a group is sorted by rule "name".
+std::vector<std::pair<std::string, std::shared_ptr<std::string>>> to_string_styles(
+	utki::span<const style> styles, //
+	const std::function<std::string(uint32_t)>& property_id_to_name,
+	const std::function<std::string(uint32_t, const property_value_base&)>& property_value_to_string
+)
+{
+	std::map<property_list*, std::shared_ptr<std::string>> props_map;
+
+	std::vector<std::pair<std::string, std::shared_ptr<std::string>>> str_styles;
+
+	for (const auto& s : styles) {
+		auto props_ptr = s.properties.get();
+		ASSERT(props_ptr)
+		auto props_iter = props_map.find(props_ptr);
+		if (props_iter == props_map.end()) {
+			auto res = props_map.insert(
+				std::make_pair(
+					props_ptr,
+					std::make_shared<std::string>(to_string(
+						*s.properties, //
+						property_id_to_name,
+						property_value_to_string
+					))
+				)
+			);
+			ASSERT(res.second)
+			props_iter = res.first;
+		}
+		ASSERT(props_iter != props_map.end())
+
+		str_styles.emplace_back(
+			get_name(s), //
+			props_iter->second
+		);
+	}
+
+	std::sort(
+		str_styles.begin(), //
+		str_styles.end(),
+		[](const auto& a, const auto& b) {
+			// sort by property_list to make consequent gropus using same property list by name within group
+			if (*a.second < *b.second) {
+				return true;
+			} else if (*a.second > *b.second) {
+				return false;
+			}
+
+			// sort by name within the group
+			return a.first < b.first;
+		}
+	);
+
+	return str_styles;
+}
+} // namespace
+
 void sheet::write(
 	papki::file& fi,
 	const std::function<std::string(uint32_t)>& property_id_to_name,
@@ -290,24 +349,11 @@ void sheet::write(
 	std::string_view indent
 ) const
 {
-	auto styles_to_save = this->styles; // copy
-
-	// TODO: make this sorting deterministic
-	// std::sort(
-	// 	styles_to_save.begin(), //
-	// 	styles_to_save.end(),
-	// 	[](const auto& a, const auto& b) -> bool {
-	// 		// sort by property_list to make consequent gropus using same property list by name within group
-	// 		if (a.properties.get() < b.properties.get()) {
-	// 			return true;
-	// 		} else if (a.properties.get() > b.properties.get()) {
-	// 			return false;
-	// 		}
-
-	// 		// sort by name within the group
-	// 		return a.get_name() < b.get_name();
-	// 	}
-	// );
+	auto styles_to_save = to_string_styles(
+		this->styles, //
+		property_id_to_name,
+		property_value_to_string
+	);
 
 	papki::file::guard file_guard(fi, papki::file::mode::create);
 
@@ -317,7 +363,7 @@ void sheet::write(
 		// such selector chains will go in a row.
 		auto selector_group_start_iter = i;
 		for (auto j = selector_group_start_iter; j != styles_to_save.end(); ++j) {
-			if (j->properties.get() != selector_group_start_iter->properties.get()) {
+			if (j->second.get() != selector_group_start_iter->second.get()) {
 				ASSERT(j > i)
 				i = --j;
 				break;
@@ -331,7 +377,7 @@ void sheet::write(
 				fi.write(utki::make_span(indent));
 			}
 
-			fi.write(get_name(*j));
+			fi.write(j->first);
 		}
 
 		// write properties
@@ -339,15 +385,9 @@ void sheet::write(
 		fi.write(utki::make_span(indent));
 		fi.write(tab_char);
 
-		ASSERT(selector_group_start_iter->properties)
-
-		auto props_str = to_string(
-			*selector_group_start_iter->properties, //
-			property_id_to_name,
-			property_value_to_string
-		);
+		ASSERT(selector_group_start_iter->second)
 
-		fi.write(props_str);
+		fi.write(*selector_group_start_iter->second);
 
 		fi.write(new_line_char);
 		fi.write(utki::make_span(indent));
diff --git a/tests/unit/samples_data/sample3.css.cmp b/tests/unit/samples_data/sample3.css.cmp
index e341bee..0cca88b 100644
--- a/tests/unit/samples_data/sample3.css.cmp
+++ b/tests/unit/samples_data/sample3.css.cmp
@@ -1,12 +1,12 @@
-.cls-1, .cls-3 {
-	fill: none; 
+.cls-4 {
+	fill-rule: evenodd; 
 }
 .cls-2, .cls-4 {
 	fill: #47506a; 
 }
+.cls-1, .cls-3 {
+	fill: none; 
+}
 .cls-3 {
 	stroke: #3866f0; stroke-width: 4px; 
 }
-.cls-4 {
-	fill-rule: evenodd; 
-}
diff --git a/tests/unit/samples_data/sample4.css.cmp b/tests/unit/samples_data/sample4.css.cmp
index 813826b..d84c7c2 100644
--- a/tests/unit/samples_data/sample4.css.cmp
+++ b/tests/unit/samples_data/sample4.css.cmp
@@ -1,6 +1,6 @@
-tag-1, tag-2 {
-	fill: #445566; 
-}
 tag-3, tag-4 {
 	fill: #334455; 
 }
+tag-1, tag-2 {
+	fill: #445566; 
+}
diff --git a/tests/unit/samples_data/sample5.css.cmp b/tests/unit/samples_data/sample5.css.cmp
index 68e505e..830bd93 100644
--- a/tests/unit/samples_data/sample5.css.cmp
+++ b/tests/unit/samples_data/sample5.css.cmp
@@ -1,6 +1,6 @@
-#id-1, #id-2 {
-	fill: #445566; 
-}
 #id-3, #id-4 {
 	fill: #334455; 
 }
+#id-1, #id-2 {
+	fill: #445566; 
+}
diff --git a/tests/unit/samples_data/sample6.css.cmp b/tests/unit/samples_data/sample6.css.cmp
index 4541327..cb84c5f 100644
--- a/tests/unit/samples_data/sample6.css.cmp
+++ b/tests/unit/samples_data/sample6.css.cmp
@@ -1,6 +1,6 @@
-.cls-1, .cls-2 {
-	fill: #445566; 
-}
 .cls-3, .cls-4 {
 	fill: #334455; 
 }
+.cls-1, .cls-2 {
+	fill: #445566; 
+}
diff --git a/tests/unit/samples_data/sample7.css.cmp b/tests/unit/samples_data/sample7.css.cmp
index aedc856..9eed867 100644
--- a/tests/unit/samples_data/sample7.css.cmp
+++ b/tests/unit/samples_data/sample7.css.cmp
@@ -1,9 +1,6 @@
-#id-1 {
+#id-1, .cls-3.cls-4, tag-1 {
 	fill: #334455; 
 }
 .cls-1.cls-2 {
 	fill: #445566; 
 }
-.cls-3.cls-4, tag-1 {
-	fill: #334455; 
-}
diff --git a/tests/unit/samples_data/sample8.css.cmp b/tests/unit/samples_data/sample8.css.cmp
index 36422ea..84c6bfd 100644
--- a/tests/unit/samples_data/sample8.css.cmp
+++ b/tests/unit/samples_data/sample8.css.cmp
@@ -1,72 +1,72 @@
-.fence {
-	fill: none; stroke: #c4e3c3; stroke-width: 1; 
+.task {
+	fill: #000; 
 }
-.shadow {
-	filter: drop-shadow(0 0 2px #000); 
+.trees {
+	fill: #144043; 
 }
-.stairs {
-	fill: #FFD700; 
+.building {
+	fill: #1a2632; 
 }
-.task {
-	fill: #000; 
+.land {
+	fill: #1f5054; 
 }
-.danger {
-	fill: red; stroke: red; stroke-width: 2; stroke-dasharray: 4,2; fill-opacity: .4; 
+.locked {
+	fill: #37414c; 
 }
-.powerline {
-	fill: none; stroke: #ffce00; stroke-width: 2; stroke-dasharray: 6,6; stroke-miterlimit: 10; 
+.water {
+	fill: #4a6b96; 
 }
-.railroad {
-	fill: none; stroke: #914833; stroke-width: 3; stroke-dasharray: 6; 
+.wood {
+	fill: #593700; 
 }
-.road_large {
-	stroke-width: 12; 
+.floor {
+	fill: #70777f; 
 }
-.road_medium {
-	stroke-width: 8; 
+.tarmac {
+	fill: #768089; 
 }
-.road_small {
-	stroke-width: 5; 
+.gravel {
+	fill: #946d3e; 
 }
-.road_gravel {
-	fill: none; stroke: #946d3e; 
+.stairs {
+	fill: #FFD700; 
 }
-.road_tarmac {
-	fill: none; stroke: #888; 
+.cement {
+	fill: #c6c2c2; 
 }
-.trees {
-	fill: #144043; 
+.rock {
+	fill: #dcd5b6; 
 }
 .map_border {
 	fill: none; stroke: #000; stroke-width: 2; 
 }
-.locked {
-	fill: #37414c; 
+.road_tarmac {
+	fill: none; stroke: #888; 
 }
-.floor {
-	fill: #70777f; 
+.railroad {
+	fill: none; stroke: #914833; stroke-width: 3; stroke-dasharray: 6; 
 }
-.building {
-	fill: #1a2632; 
+.road_gravel {
+	fill: none; stroke: #946d3e; 
 }
-.gravel {
-	fill: #946d3e; 
+.fence {
+	fill: none; stroke: #c4e3c3; stroke-width: 1; 
 }
-.tarmac {
-	fill: #768089; 
+.powerline {
+	fill: none; stroke: #ffce00; stroke-width: 2; stroke-dasharray: 6,6; stroke-miterlimit: 10; 
 }
-.wood {
-	fill: #593700; 
+.danger {
+	fill: red; stroke: red; stroke-width: 2; stroke-dasharray: 4,2; fill-opacity: .4; 
 }
-.water {
-	fill: #4a6b96; 
+.shadow {
+	filter: drop-shadow(0 0 2px #000); 
 }
-.rock {
-	fill: #dcd5b6; 
+.road_large {
+	stroke-width: 12; 
 }
-.land {
-	fill: #1f5054; 
+.road_small {
+	stroke-width: 5; 
 }
-.cement {
-	fill: #c6c2c2; 
+.road_medium {
+	stroke-width: 8; 
 }
diff --git a/tests/unit/samples_data/simple0.css.cmp b/tests/unit/samples_data/simple0.css.cmp
index 0ea056a..c1ef706 100644
--- a/tests/unit/samples_data/simple0.css.cmp
+++ b/tests/unit/samples_data/simple0.css.cmp
@@ -1,6 +1,6 @@
-body h1 {
+body {
 	background-color: green; 
 }
-body {
+body h1 {
 	background-color: green; 
 }
diff --git a/tests/unit/samples_data/simple1.css.cmp b/tests/unit/samples_data/simple1.css.cmp
index 3f7bb41..02a95ef 100644
--- a/tests/unit/samples_data/simple1.css.cmp
+++ b/tests/unit/samples_data/simple1.css.cmp
@@ -1,12 +1,12 @@
-body.foo h1.bar {
+.foo {
 	background-color: green; 
 }
-body.foo.bar {
+.foo h1.bar {
 	background-color: green; 
 }
-.foo h1.bar {
+body.foo h1.bar {
 	background-color: green; 
 }
-.foo {
+body.foo.bar {
 	background-color: green; 
 }