diff --git a/src/main/java/org/squiddev/cobalt/lib/StringMatch.java b/src/main/java/org/squiddev/cobalt/lib/StringMatch.java
index acbf78cb..706e2d55 100644
--- a/src/main/java/org/squiddev/cobalt/lib/StringMatch.java
+++ b/src/main/java/org/squiddev/cobalt/lib/StringMatch.java
@@ -673,7 +673,7 @@ int end_capture(int soff, int poff) throws LuaError {
 		int match_capture(int soff, int l) throws LuaError {
 			l = check_capture(l);
 			int len = clen[l];
-			if ((s.length() - soff) >= len &&
+			if (len >= 0 && (s.length() - soff) >= len &&
 				LuaString.equals(s, cinit[l], s, soff, len)) {
 				return soff + len;
 			} else {
diff --git a/src/test/resources/spec/string_spec.lua b/src/test/resources/spec/string_spec.lua
index 35a34c0a..82e1636c 100644
--- a/src/test/resources/spec/string_spec.lua
+++ b/src/test/resources/spec/string_spec.lua
@@ -130,6 +130,10 @@ describe("The string library", function()
 			expect(result):eq("HELLO WORLD")
 			expect(count):eq(10)
 		end)
+
+		it("no out-of-bounds with () (issue #78)", function()
+			string.gsub("foo", "()(%1)", "")
+		end)
 	end)
 
 	describe("string.len", function()