diff --git a/js/id/renderer/map.js b/js/id/renderer/map.js
index 2b98c491a..11b6e2e8a 100644
--- a/js/id/renderer/map.js
+++ b/js/id/renderer/map.js
@@ -15,9 +15,6 @@ iD.Map = function() {
         notice,
         background = iD.Background()
             .projection(projection),
-        class_stroke = iD.Style.styleClasses('way line stroke'),
-        class_casing = iD.Style.styleClasses('way line casing'),
-        class_area = iD.Style.styleClasses('way area'),
         transformProp = iD.util.prefixCSSProperty('Transform'),
         supersurface, surface, defs, tilegroup, r, g, alength;
 
@@ -193,25 +190,30 @@ iD.Map = function() {
         notice.message('');
     }
 
-    function drawLines(data, filter, group, class_gen) {
+    function drawLines(data, filter, group, fixedClasses) {
         var lines = group.selectAll('path')
             .filter(filter)
             .data(data, key);
+
         lines.exit().remove();
-        lines.enter().append('path');
+
+        lines.enter().append('path')
+            .attr('class', fixedClasses);
+
         lines
             .order()
             .attr('d', getline)
-            .attr('class', class_gen);
+            .call(iD.Style.styleClasses());
+
         return lines;
     }
 
     function drawFills(areas, filter) {
-        drawLines(areas, filter, g.fill, class_area);
+        drawLines(areas, filter, g.fill, 'way area');
     }
 
     function drawCasings(ways, filter) {
-        drawLines(ways, filter, g.casing, class_casing);
+        drawLines(ways, filter, g.casing, 'way line casing');
     }
 
     function drawPoints(points, filter) {
@@ -242,7 +244,7 @@ iD.Map = function() {
     }
 
     function drawStrokes(ways, filter) {
-        var strokes = drawLines(ways, filter, g.stroke, class_stroke);
+        var strokes = drawLines(ways, filter, g.stroke, 'way line stroke');
 
         // Determine the lengths of oneway paths
         var lengths = {},
diff --git a/js/id/renderer/style.js b/js/id/renderer/style.js
index 4c35c5650..99b346329 100644
--- a/js/id/renderer/style.js
+++ b/js/id/renderer/style.js
@@ -53,15 +53,26 @@ iD.Style.TAG_CLASSES = iD.util.trueObj([
     'landuse', 'building', 'oneway', 'bridge'
 ]);
 
-iD.Style.styleClasses = function(pre) {
-    return function(d) {
-        var tags = d.tags;
-        var c = pre ? [pre] : [];
-        for (var k in tags) {
-            if (!iD.Style.TAG_CLASSES[k]) continue;
-            c.push('tag-' + k);
-            c.push('tag-' + k + '-' + tags[k]);
-        }
-        return c.join(' ');
+iD.Style.styleClasses = function() {
+    var tagClassRe = /^tag-/;
+    return function(selection) {
+        selection.each(function(d) {
+            var classes, value = this.className;
+
+            if (value.baseVal != null) value = value.baseVal;
+
+            classes = value.trim().split(/\s+/).filter(function(name) {
+                return name.length && !tagClassRe.test(name);
+            });
+
+            var tags = d.tags;
+            for (var k in tags) {
+                if (!iD.Style.TAG_CLASSES[k]) continue;
+                classes.push('tag-' + k);
+                classes.push('tag-' + k + '-' + tags[k]);
+            }
+
+            return selection.attr('class', classes.join(' '));
+        });
     };
 };
diff --git a/test/spec/renderer/style.js b/test/spec/renderer/style.js
index b48554c84..1fccc9658 100644
--- a/test/spec/renderer/style.js
+++ b/test/spec/renderer/style.js
@@ -16,22 +16,48 @@ describe('iD.Style', function() {
     });
 
     describe('#styleClasses', function() {
-        it('returns an empty string when no classes are present', function() {
-            var classes = iD.Style.styleClasses(''),
-                entity = iD.Entity();
-            expect(classes(entity)).to.equal('');
+        var selection;
+
+        beforeEach(function () {
+            selection = d3.select(document.createElement('div'));
         });
 
-        it('returns a string containing predefined classes', function() {
-            var classes = iD.Style.styleClasses('selected'),
-                entity = iD.Entity();
-            expect(classes(entity)).to.equal('selected');
+        it('adds no classes to elements whose datum has no tags', function() {
+            selection
+                .datum(iD.Entity())
+                .call(iD.Style.styleClasses());
+            expect(selection.attr('class')).to.equal('');
         });
 
-        it('returns a string containing classes for highway tags', function() {
-            var classes = iD.Style.styleClasses(''),
-                entity = iD.Entity({tags: {highway: 'primary'}});
-            expect(classes(entity)).to.equal('tag-highway tag-highway-primary');
+        it('adds classes for highway tags', function() {
+            selection
+                .datum(iD.Entity({tags: {highway: 'primary'}}))
+                .call(iD.Style.styleClasses());
+            expect(selection.attr('class')).to.equal('tag-highway tag-highway-primary');
+        });
+
+        it('removes classes for tags that are no longer present', function() {
+            selection
+                .attr('class', 'tag-highway tag-highway-primary')
+                .datum(iD.Entity())
+                .call(iD.Style.styleClasses());
+            expect(selection.attr('class')).to.equal('');
+        });
+
+        it('preserves existing non-"tag-"-prefixed classes', function() {
+            selection
+                .attr('class', 'selected')
+                .datum(iD.Entity())
+                .call(iD.Style.styleClasses());
+            expect(selection.attr('class')).to.equal('selected');
+        });
+
+        it('works on SVG elements', function() {
+            selection = d3.select(document.createElementNS('http://www.w3.org/2000/svg', 'g'));
+            selection
+                .datum(iD.Entity())
+                .call(iD.Style.styleClasses());
+            expect(selection.attr('class')).to.equal('');
         });
     });
 });