diff --git a/luaj-core/src/main/java/org/luaj/vm2/lib/StringLib.java b/luaj-core/src/main/java/org/luaj/vm2/lib/StringLib.java
index 713ab9be..c2351f3e 100644
--- a/luaj-core/src/main/java/org/luaj/vm2/lib/StringLib.java
+++ b/luaj-core/src/main/java/org/luaj/vm2/lib/StringLib.java
@@ -640,6 +640,8 @@ public class StringLib extends TwoArgFunction {
 			int lastmatch = -1; /* end of last match */
 			LuaValue repl = args.arg(3);
 			int max_s = args.optint(4, srclen+1);
+			if (max_s < 0)
+				max_s = srclen+1;
 			final boolean anchor = p.length() > 0 && p.charAt(0) == '^';
 
 			Buffer lbuf = new Buffer(srclen);
diff --git a/luaj-test/src/test/resources/compatibility/jme/stringlib.out b/luaj-test/src/test/resources/compatibility/jme/stringlib.out
index 7ebe326d..9cb6e786 100644
Binary files a/luaj-test/src/test/resources/compatibility/jme/stringlib.out and b/luaj-test/src/test/resources/compatibility/jme/stringlib.out differ
diff --git a/luaj-test/src/test/resources/compatibility/jse/stringlib.out b/luaj-test/src/test/resources/compatibility/jse/stringlib.out
index 7ebe326d..9cb6e786 100644
Binary files a/luaj-test/src/test/resources/compatibility/jse/stringlib.out and b/luaj-test/src/test/resources/compatibility/jse/stringlib.out differ
diff --git a/luaj-test/src/test/resources/compatibility/luajit/stringlib.out b/luaj-test/src/test/resources/compatibility/luajit/stringlib.out
index 7ebe326d..3ffabfe0 100644
Binary files a/luaj-test/src/test/resources/compatibility/luajit/stringlib.out and b/luaj-test/src/test/resources/compatibility/luajit/stringlib.out differ
diff --git a/luaj-test/src/test/resources/compatibility/stringlib.lua b/luaj-test/src/test/resources/compatibility/stringlib.lua
index dbaf1931..40de55d0 100644
--- a/luaj-test/src/test/resources/compatibility/stringlib.lua
+++ b/luaj-test/src/test/resources/compatibility/stringlib.lua
@@ -21,6 +21,9 @@ print( string.match( "abbaaababaabaaabaa", "b(a*)()b", 12 ) )
 
 print( string.byte("hi", -3) )
 
+print( string.gsub("ABC ABC ABC", "ABC", "DEF", -1) )
+print( string.gsub("ABC ABC ABC", "ABC", "DEF", 0) )
+print( string.gsub("ABC ABC ABC", "ABC", "DEF", 2) )
 print( string.gsub("ABC", "@(%x+)", function(s) return "|abcd" end) )
 print( string.gsub("@123", "@(%x+)", function(s) return "|abcd" end) )
 print( string.gsub("ABC@123", "@(%x+)", function(s) return "|abcd" end) )