--- a/devtools/client/shared/test/unit/test_rewriteDeclarations.js
+++ b/devtools/client/shared/test/unit/test_rewriteDeclarations.js
@@ -520,16 +520,25 @@ const TEST_DATA = [
 
   {
     desc: "function regression test for bug 1321970",
     input: "",
     instruction: {type: "create", name: "p", value: "func(1,2)", priority: "",
                   index: 0, enabled: true},
     expected: "p: func(1,2);",
   },
+
+  {
+    desc: "function regression test for bug 1355233",
+    input: "",
+    instruction: {type: "create", name: "p", value: "func(", priority: "",
+                  index: 0, enabled: true},
+    expected: "p: func\\(;",
+    changed: {0: "func\\("}
+  },
 ];
 
 function rewriteDeclarations(inputString, instruction, defaultIndentation) {
   let rewriter = new RuleRewriter(isCssPropertyKnown, null, inputString);
   rewriter.defaultIndentation = defaultIndentation;
 
   switch (instruction.type) {
     case "rename":

--- a/devtools/shared/css/parsing-utils.js
+++ b/devtools/shared/css/parsing-utils.js
@@ -611,19 +611,22 @@ RuleRewriter.prototype = {
 
     let result = "";
     let previousOffset = 0;
     let parenStack = [];
     let anySanitized = false;
 
     // Push a closing paren on the stack.
     let pushParen = (token, closer) => {
-      result += text.substring(previousOffset, token.startOffset);
-      parenStack.push({closer, offset: result.length});
-      result += text.substring(token.startOffset, token.endOffset);
+      result = result + text.substring(previousOffset, token.startOffset) +
+        text.substring(token.startOffset, token.endOffset);
+      // We set the location of the paren in a funny way, to handle
+      // the case where we've seen a function token, where the paren
+      // appears at the end.
+      parenStack.push({closer, offset: result.length - 1});
       previousOffset = token.endOffset;
     };
 
     // Pop a closing paren from the stack.
     let popSomeParens = (closer) => {
       while (parenStack.length > 0) {
         let paren = parenStack.pop();