diff --git a/dlls/jscript/string.c b/dlls/jscript/string.c
index 927d95ab9e5..efdff177cec 100644
--- a/dlls/jscript/string.c
+++ b/dlls/jscript/string.c
@@ -393,8 +393,10 @@ static HRESULT String_fontcolor(DispatchEx *dispex, LCID lcid, WORD flags, DISPP
 static HRESULT String_fontsize(DispatchEx *dispex, LCID lcid, WORD flags, DISPPARAMS *dp,
         VARIANT *retv, jsexcept_t *ei, IServiceProvider *sp)
 {
-    FIXME("\n");
-    return E_NOTIMPL;
+    static const WCHAR fontW[] = {'F','O','N','T',0};
+    static const WCHAR colorW[] = {'S','I','Z','E',0};
+
+    return do_attribute_tag_format(dispex, lcid, flags, dp, retv, ei, sp, fontW, colorW);
 }
 
 static HRESULT String_indexOf(DispatchEx *dispex, LCID lcid, WORD flags, DISPPARAMS *dp,
diff --git a/dlls/jscript/tests/api.js b/dlls/jscript/tests/api.js
index 2368a4bd521..fe2093981a0 100644
--- a/dlls/jscript/tests/api.js
+++ b/dlls/jscript/tests/api.js
@@ -318,6 +318,22 @@ ok(tmp === "<FONT COLOR=\"3\">test</FONT>", "'test'.fontcolor(3) = " + tmp);
 tmp = "test".fontcolor("green");
 ok(tmp === "<FONT COLOR=\"green\">test</FONT>", "'test'.fontcolor('green') = " + tmp);
 
+tmp = "".fontsize();
+ok(tmp === "<FONT SIZE=\"undefined\"></FONT>", "''.fontsize() = " + tmp);
+tmp = "".fontsize(3);
+ok(tmp === "<FONT SIZE=\"3\"></FONT>", "''.fontsize(3) = " + tmp);
+tmp = "".fontsize("red");
+ok(tmp === "<FONT SIZE=\"red\"></FONT>", "''.fontsize('red') = " + tmp);
+tmp = "test".fontsize();
+ok(tmp === "<FONT SIZE=\"undefined\">test</FONT>", "'test'.fontsize() = " + tmp);
+tmp = "test".fontsize(3);
+ok(tmp === "<FONT SIZE=\"3\">test</FONT>", "'test'.fontsize(3) = " + tmp);
+tmp = "test".fontsize("green");
+ok(tmp === "<FONT SIZE=\"green\">test</FONT>", "'test'.fontsize('green') = " + tmp);
+
+tmp = ("".fontcolor()).fontsize();
+ok(tmp === "<FONT SIZE=\"undefined\"><FONT COLOR=\"undefined\"></FONT></FONT>", "(''.fontcolor()).fontsize() = " + tmp);
+
 tmp = "".italics();
 ok(tmp === "<I></I>", "''.italics() = " + tmp);
 tmp = "".italics(3);