diff --git a/apps/src/gamelab/GameLab.js b/apps/src/gamelab/GameLab.js
index bf35be24e9272..91a9060ebcc65 100644
--- a/apps/src/gamelab/GameLab.js
+++ b/apps/src/gamelab/GameLab.js
@@ -945,13 +945,15 @@ GameLab.prototype.initInterpreter = function(attachDebugger = true) {
   if (this.level.customHelperLibrary) {
     code += this.level.customHelperLibrary + '\n';
   }
+  const userCodeStartOffset = code.length;
   code += this.studioApp_.getCode();
   this.JSInterpreter.parse({
     code,
     blocks: dropletConfig.blocks,
     blockFilter: this.level.executePaletteApisOnly && this.level.codeFunctions,
     enableEvents: true,
-    initGlobals: injectGamelabGlobals
+    initGlobals: injectGamelabGlobals,
+    userCodeStartOffset
   });
   if (!this.JSInterpreter.initialized()) {
     return;
diff --git a/apps/src/lib/tools/jsinterpreter/JSInterpreter.js b/apps/src/lib/tools/jsinterpreter/JSInterpreter.js
index 50dbde7cc6ac5..0fdcc386d8284 100644
--- a/apps/src/lib/tools/jsinterpreter/JSInterpreter.js
+++ b/apps/src/lib/tools/jsinterpreter/JSInterpreter.js
@@ -130,9 +130,13 @@ export default class JSInterpreter {
    * @param {Function} [options.initGlobals] when supplied, this function will
    *        be called during interpreter initialization so that additional globals
    *        can be added with calls to createGlobalProperty()
+   * @param {number} [options.userCodeStartOffset] - offset in the code string where
+   *        the user's created code begins. Allows other code to be injected before
+   *        the user's program without disrupting line number calculations for
+   *        debugging (default 0)
    */
   parse(options) {
-    this.calculateCodeInfo(options.code);
+    this.calculateCodeInfo(options);
 
     if (!this.studioApp.hideSource && this.studioApp.editor) {
       const session = this.studioApp.editor.aceEditor.getSession();
@@ -239,14 +243,22 @@ export default class JSInterpreter {
 
   /**
    * Init `this.codeInfo` with cumulative length info (used to locate breakpoints).
-   * @param code
+   * @param {!Object} options
+   * @param {!string} options.code - Code to be executed by the interpreter.
+   * @param {number} [options.userCodeStartOffset] - offset in the code string where
+   *        the user's created code begins. Allows other code to be injected before
+   *        the user's program without disrupting line number calculations for
+   *        debugging (default 0)
    */
-  calculateCodeInfo(code) {
+  calculateCodeInfo(options) {
+    const {code, userCodeStartOffset = 0} = options;
     this.codeInfo = {};
     this.codeInfo.code = code;
-    this.codeInfo.userCodeStartOffset = 0;
-    this.codeInfo.userCodeLength = code.length;
-    this.codeInfo.cumulativeLength = codegen.calculateCumulativeLength(code);
+    this.codeInfo.userCodeStartOffset = userCodeStartOffset;
+    this.codeInfo.userCodeLength = code.length - userCodeStartOffset;
+    this.codeInfo.cumulativeLength = codegen.calculateCumulativeLength(
+      code.slice(userCodeStartOffset)
+    );
   }
 
   /**
diff --git a/apps/test/unit/lib/tools/jsdebugger/DebugConsoleTest.js b/apps/test/unit/lib/tools/jsdebugger/DebugConsoleTest.js
index dfaed13195c37..1a6a76e3b1853 100644
--- a/apps/test/unit/lib/tools/jsdebugger/DebugConsoleTest.js
+++ b/apps/test/unit/lib/tools/jsdebugger/DebugConsoleTest.js
@@ -140,7 +140,7 @@ describe('The DebugConsole component', () => {
         studioApp: {hideSource: true}
       });
       const code = '0;\n1;\n2;\n3;\n4;\n5;\n6;\n7;';
-      interpreter.calculateCodeInfo(code);
+      interpreter.calculateCodeInfo({code});
       interpreter.parse({code});
       interpreter.paused = true;
       interpreter.nextStep = JSInterpreter.StepType.IN;
diff --git a/apps/test/unit/lib/tools/jsdebugger/reduxTest.js b/apps/test/unit/lib/tools/jsdebugger/reduxTest.js
index 30247628012fa..2356532f61805 100644
--- a/apps/test/unit/lib/tools/jsdebugger/reduxTest.js
+++ b/apps/test/unit/lib/tools/jsdebugger/reduxTest.js
@@ -44,7 +44,7 @@ describe('The JSDebugger redux duck', () => {
 
   function runToBreakpoint() {
     const code = '0;\n1;\n2;\n3;\n4;\n5;\n6;\n7;';
-    interpreter.calculateCodeInfo(code);
+    interpreter.calculateCodeInfo({code});
     interpreter.parse({code});
     interpreter.paused = true;
     interpreter.nextStep = JSInterpreter.StepType.IN;
diff --git a/apps/test/unit/lib/tools/jsinterpreter/JSInterpreterTest.js b/apps/test/unit/lib/tools/jsinterpreter/JSInterpreterTest.js
index 58f7431b819f4..87496d269c1cb 100644
--- a/apps/test/unit/lib/tools/jsinterpreter/JSInterpreterTest.js
+++ b/apps/test/unit/lib/tools/jsinterpreter/JSInterpreterTest.js
@@ -18,7 +18,7 @@ describe('The JSInterpreter class', function() {
     });
 
     // Initialize a test program
-    jsInterpreter.calculateCodeInfo(code);
+    jsInterpreter.calculateCodeInfo({code});
     jsInterpreter.parse({code: code});
 
     assert(jsInterpreter.initialized());