diff --git a/build.py b/build.py
index c1331ca9c..0647a0f69 100755
--- a/build.py
+++ b/build.py
@@ -56,6 +56,9 @@ else:
   from urllib.parse import urlencode
   from importlib import reload
 
+# Read package.json and extract the current Blockly version.
+blocklyVersion = json.loads(open('package.json', 'r').read())['version']
+
 def import_path(fullpath):
   """Import a file with full path specification.
   Allows one to import from any directory, something __import__ does not do.
@@ -221,7 +224,11 @@ class Gen_compressed(threading.Thread):
       if filename.startswith(os.pardir + os.sep):  # '../'
         continue
       f = codecs.open(filename, encoding="utf-8")
-      params.append(("js_code", "".join(f.readlines()).encode("utf-8")))
+      code = "".join(f.readlines()).encode("utf-8")
+      # Inject the Blockly version.
+      if filename == "core/blockly.js":
+        code = code.replace("Blockly.VERSION = 'uncompiled';", "Blockly.VERSION = '" + blocklyVersion + "';")
+      params.append(("js_code", code))
       f.close()
 
     self.do_compile(params, target_filename, filenames, "")
diff --git a/core/blockly.js b/core/blockly.js
index 6e3a3ddd8..123ab8c57 100644
--- a/core/blockly.js
+++ b/core/blockly.js
@@ -65,6 +65,16 @@ goog.require('Blockly.Xml');
 var CLOSURE_DEFINES = {'goog.DEBUG': false};
 /* eslint-enable no-unused-vars */
 
+/**
+ * Blockly core version.
+ * This constant is overriden by the build script (build.py) to the value of the version
+ * in package.json. This is done during the gen_core build step.
+ * For local builds, you can pass --define='Blockly.VERSION=X.Y.Z' to the compiler
+ * to override this constant.
+ * @define {string}
+ */
+Blockly.VERSION = 'uncompiled';
+
 /**
  * The main workspace most recently used.
  * Set by Blockly.WorkspaceSvg.prototype.markFocused