diff --git a/serial.js b/serial.js
index 56b8c8d..aae8a47 100644
--- a/serial.js
+++ b/serial.js
@@ -237,17 +237,21 @@ var $serial = (typeof(exports) !== 'undefined') ? exports : {};
 			current.default.textSize = serializeProp(props, "f", key.default.textSize, current.default.textSize);
 			if(props.f) current.textSize = [];
 			if(!compareTextSizes(current.textSize, ordered.textSize, ordered.labels)) {
-				var optimizeF2 = !ordered.textSize[0];
-				for(var i = 2; i < ordered.textSize.length && optimizeF2; ++i) {
-					optimizeF2 = (ordered.textSize[i] == ordered.textSize[1]);
-				}
-				if(optimizeF2) {
-					var f2 = ordered.textSize[1];
-					current.f2 = serializeProp(props, "f2", f2, -1);
-					current.textSize = [0,f2,f2,f2,f2,f2,f2,f2,f2,f2,f2,f2];
+				if(ordered.textSize.length == 0) {
+					serializeProp(props, "f", key.default.textSize, -1); // Force 'f' to be written
 				} else {
-					current.f2 = undefined;
-					current.textSize = serializeProp(props, "fa", ordered.textSize, []);
+					var optimizeF2 = !ordered.textSize[0];
+					for(var i = 2; i < ordered.textSize.length && optimizeF2; ++i) {
+						optimizeF2 = (ordered.textSize[i] == ordered.textSize[1]);
+					}
+					if(optimizeF2) {
+						var f2 = ordered.textSize[1];
+						current.f2 = serializeProp(props, "f2", f2, -1);
+						current.textSize = [0,f2,f2,f2,f2,f2,f2,f2,f2,f2,f2,f2];
+					} else {
+						current.f2 = undefined;
+						current.textSize = serializeProp(props, "fa", ordered.textSize, []);
+					}
 				}
 			}
 			serializeProp(props, "w", key.width, 1);
diff --git a/spec/kb-serial-spec.js b/spec/kb-serial-spec.js
index 223ebcf..e56f6ba 100644
--- a/spec/kb-serial-spec.js
+++ b/spec/kb-serial-spec.js
@@ -98,6 +98,12 @@ describe('keyboard serialization', function() {
       expect($serial.serialize(kbd)).toEqual(original);
     });
 
+    it('should write "f" to reset back to default, even if default didn\'t change', function() {
+      var original = [[{f2:5},"X\nY",{f:3}, "X\nY"]];
+      var kbd = $serial.deserialize(original);
+      expect($serial.serialize(kbd)).toEqual(original);
+    });
+
     it('should handle "fa"', function() {
       for(var align = 0; align < 7; ++align) {
         var original = [ [{f:1,fa:[1,2,3,4,5,6,7,8,9,10,11,12],a:align}, '1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12'] ];