diff --git a/poky/documentation/sphinx/yocto-vars.py b/poky/documentation/sphinx/yocto-vars.py
index 5689472..8083d7d 100644
--- a/poky/documentation/sphinx/yocto-vars.py
+++ b/poky/documentation/sphinx/yocto-vars.py
@@ -1,10 +1,19 @@
 #!/usr/bin/env python
 import re
-import yaml
+import sys
 
 import sphinx
 from sphinx.application import Sphinx
 
+# This extension uses pyyaml, report an explicit
+# error message if it's not installed
+try:
+    import yaml
+except ImportError:
+    sys.stderr.write("The Yocto Project Sphinx documentation requires PyYAML.\
+    \nPlease make sure to install pyyaml python package.\n")
+    sys.exit(1)
+
 __version__  = '1.0'
 
 # Variables substitutions. Uses {VAR} subst using variables defined in poky.yaml