diff --git a/Docs/Changelog_sm5.txt b/Docs/Changelog_sm5.txt
index 7e5ff65cc4..0ec0d5ad7a 100644
--- a/Docs/Changelog_sm5.txt
+++ b/Docs/Changelog_sm5.txt
@@ -4,6 +4,14 @@ The StepMania 5 Changelog covers all post-sm-ssc changes. For a list of changes
 from StepMania 4 alpha 5 to sm-ssc v1.2.5, see Changelog_sm-ssc.txt.
 ________________________________________________________________________________
 
+2015/04/02
+----------
+* [global] commify function exposed to lua. [kyzentun]
+
+================================================================================
+StepMania 5.0.7 | 20150401
+--------------------------------------------------------------------------------
+
 2015/03/30
 ----------
 * [Select Music] Ctrl+Shift+R mapped to reload the current song. [kyzentun]
diff --git a/Docs/Luadoc/Lua.xml b/Docs/Luadoc/Lua.xml
index 7cc8733d3f..35f2706c47 100644
--- a/Docs/Luadoc/Lua.xml
+++ b/Docs/Luadoc/Lua.xml
@@ -209,6 +209,7 @@
 		<Function name='class'/>
 		<Function name='collectgarbage'/>
 		<Function name='color'/>
+		<Function name='commify'/>
 		<Function name='dofile'/>
 		<Function name='error'/>
 		<Function name='fapproach'/>
diff --git a/Docs/Luadoc/LuaDocumentation.xml b/Docs/Luadoc/LuaDocumentation.xml
index 30255d2bce..2546f90afe 100644
--- a/Docs/Luadoc/LuaDocumentation.xml
+++ b/Docs/Luadoc/LuaDocumentation.xml
@@ -109,6 +109,15 @@ save yourself some time, copy this for undocumented things:
 	<Function name='ComboUnderField' theme='_fallback' return='bool' arguments=''>
 		[03 Gameplay.lua] Returns the <code>UserPrefComboUnderField</code> user preference value.
 	</Function>
+	<Function name='commify' return='string' arguments='string number, string comma, string dot'>
+		This will take the number and insert a comma every three digits, as normal in English for writing large numbers.<br />
+		<code>number</code> can be a string, an integer, or a float.<br />
+		<code>comma</code> is an optional argument that is used instead of a comma.<br />
+		"commify(1234, 'cat')" will result in "1cat234".<br />
+		<code>dot</code> is an optional argument that is used instead of a dot to find the end of the part that should be commified.<br />
+		"commify('1234cat5678', ',', 'cat')" will result in "1,234cat5678", but "commify('1234cat5678')" will result in "12,34c,at5,678".<br />
+		The <code>comma</code> and <code>dot</code> arguments are provided to ease compliance with locales or languages that do not use comma and dot in numbers the way English does.
+	</Function>
 	<Function name='ConnectToServer' return='bool' arguments='string sAddress'>
 		Tries to connect to the server at <code>sAddress</code>.
 	</Function>
diff --git a/Themes/_fallback/Scripts/00 init.lua b/Themes/_fallback/Scripts/00 init.lua
index a3c353f946..50bfa04d4d 100644
--- a/Themes/_fallback/Scripts/00 init.lua	
+++ b/Themes/_fallback/Scripts/00 init.lua	
@@ -60,11 +60,7 @@ function split(delimiter, text)
 end
 
 function join(delimiter, list)
-	local ret = list[1]
-	for i = 2,table.getn(list) do
-		ret = ret .. delimiter .. list[i]
-	end
-	return ret or ""
+	return table.concat(list, delimiter)
 end
 
 -- (c) 2006 Glenn Maynard
diff --git a/src/RageUtil.cpp b/src/RageUtil.cpp
index ea10ac5fb3..fddc281f9a 100644
--- a/src/RageUtil.cpp
+++ b/src/RageUtil.cpp
@@ -332,17 +332,39 @@ RString Commify( int iNum )
 	return Commify( sNum );
 }
 
-RString Commify( RString sNum, RString sSeperator ) 
+RString Commify(const RString& num, const RString& sep, const RString& dot)
 {
-	RString sReturn;
-	for( unsigned i=0; i<sNum.length(); i++ )
+	size_t num_end= num.size();
+	size_t dot_pos= num.find(dot);
+	if(dot_pos != string::npos)
 	{
-		char cDigit = sNum[sNum.length()-1-i];
-		if( i!=0 && i%3 == 0 )
-			sReturn = sSeperator + sReturn;
-		sReturn = cDigit + sReturn;
+		num_end= dot_pos;
 	}
-	return sReturn;
+	size_t commies= (num_end / 3) - (!(num_end % 3));
+	if(commies < 1)
+	{
+		return num;
+	}
+	size_t commified_len= num.size() + (commies * sep.size());
+	RString ret;
+	ret.resize(commified_len);
+	size_t dest= 0;
+	size_t next_comma= (num_end % 3) + (3 * (!(num_end % 3)));
+	for(size_t c= 0; c < num.size(); ++c)
+	{
+		if(c == next_comma && c < num_end)
+		{
+			for(size_t s= 0; s < sep.size(); ++s)
+			{
+				ret[dest]= sep[s];
+				++dest;
+			}
+			next_comma+= 3;
+		}
+		ret[dest]= num[c];
+		++dest;
+	}
+	return ret;
 }
 
 static LocalizedString NUM_PREFIX	( "RageUtil", "NumPrefix" );
@@ -2396,6 +2418,26 @@ static bool UndocumentedFeature( RString s ){ sm_crash(s); return true; }
 LuaFunction( UndocumentedFeature, UndocumentedFeature(SArg(1)) );
 LuaFunction( lerp, lerp(FArg(1), FArg(2), FArg(3)) );
 
+int LuaFunc_commify(lua_State* L);
+int LuaFunc_commify(lua_State* L)
+{
+	RString num= SArg(1);
+	RString sep= ",";
+	RString dot= ".";
+	if(!lua_isnoneornil(L, 2))
+	{
+		sep= lua_tostring(L, 2);
+	}
+	if(!lua_isnoneornil(L, 3))
+	{
+		dot= lua_tostring(L, 3);
+	}
+	RString ret= Commify(num, sep, dot);
+	LuaHelpers::Push(L, ret);
+	return 1;
+}
+LUAFUNC_REGISTER_COMMON(commify);
+
 void luafunc_approach_internal(lua_State* L, int valind, int goalind, int speedind);
 void luafunc_approach_internal(lua_State* L, int valind, int goalind, int speedind, int process_index)
 {
diff --git a/src/RageUtil.h b/src/RageUtil.h
index 5e4368f470..8a04ac8c4c 100644
--- a/src/RageUtil.h
+++ b/src/RageUtil.h
@@ -360,7 +360,7 @@ RString SecondsToMMSS( float fSecs );
 RString PrettyPercent( float fNumerator, float fDenominator );
 inline RString PrettyPercent( int fNumerator, int fDenominator ) { return PrettyPercent( float(fNumerator), float(fDenominator) ); }
 RString Commify( int iNum );
-RString Commify( RString sNum, RString sSeperator = "," );
+RString Commify(const RString& num, const RString& sep= ",", const RString& dot= ".");
 RString FormatNumberAndSuffix( int i );