diff --git a/src/calibre/ebooks/metadata/__init__.py b/src/calibre/ebooks/metadata/__init__.py
index ab9858b5ff..246ba0db73 100644
--- a/src/calibre/ebooks/metadata/__init__.py
+++ b/src/calibre/ebooks/metadata/__init__.py
@@ -386,3 +386,36 @@ class MetaInformation(object):
 
     def __nonzero__(self):
         return bool(self.title or self.author or self.comments or self.tags)
+
+def check_isbn10(isbn):
+    try:
+        digits = map(int, isbn[:9])
+        products = [(i+1)*digits[i] for i in range(9)]
+        check = sum(products)%11
+        if (check == 10 and isbn[9] == 'X') or check == int(isbn[9]):
+            return isbn
+    except:
+        pass
+    return None
+
+def check_isbn13(isbn):
+    try:
+        digits = map(int, isbn[:12])
+        products = [(1 if i%2 ==0 else 3)*digits[i] for i in range(12)]
+        check = 10 - (sum(products)%10)
+        if check == 10:
+            check = 0
+        if str(check) == isbn[12]:
+            return isbn
+    except:
+        pass
+    return None
+
+def check_isbn(isbn):
+    isbn = re.sub(r'[^0-9X]', '', isbn).upper()
+    if len(isbn) == 10:
+        return check_isbn10(isbn)
+    if len(isbn) == 13:
+        return check_isbn13(isbn)
+    return None
+
diff --git a/src/calibre/gui2/dialogs/metadata_single.py b/src/calibre/gui2/dialogs/metadata_single.py
index 20a3d2a480..435c0b40cd 100644
--- a/src/calibre/gui2/dialogs/metadata_single.py
+++ b/src/calibre/gui2/dialogs/metadata_single.py
@@ -23,7 +23,8 @@ from calibre.gui2.dialogs.fetch_metadata import FetchMetadata
 from calibre.gui2.dialogs.tag_editor import TagEditor
 from calibre.gui2.widgets import ProgressIndicator
 from calibre.ebooks import BOOK_EXTENSIONS
-from calibre.ebooks.metadata import authors_to_sort_string, string_to_authors, authors_to_string
+from calibre.ebooks.metadata import authors_to_sort_string, string_to_authors, \
+        authors_to_string, check_isbn
 from calibre.ebooks.metadata.library_thing import cover_from_isbn
 from calibre import islinux
 from calibre.ebooks.metadata.meta import get_metadata
@@ -336,6 +337,7 @@ class MetadataSingleDialog(ResizableDialog, Ui_MetadataSingleDialog):
         isbn = db.isbn(self.id, index_is_id=True)
         if not isbn:
             isbn = ''
+        self.isbn.textChanged.connect(self.validate_isbn)
         self.isbn.setText(isbn)
         aus = self.db.author_sort(row)
         self.author_sort.setText(aus if aus else '')
@@ -394,6 +396,20 @@ class MetadataSingleDialog(ResizableDialog, Ui_MetadataSingleDialog):
                 self.cover.setPixmap(pm)
             self.cover_data = cover
 
+    def validate_isbn(self, isbn):
+        isbn = unicode(isbn).strip()
+        if not isbn:
+            self.isbn.setStyleSheet('QLineEdit { background-color: rgba(0,255,0,0%) }')
+            self.isbn.setToolTip(_('This ISBN number is valid'))
+            return
+
+        if check_isbn(isbn):
+            self.isbn.setStyleSheet('QLineEdit { background-color: rgba(0,255,0,20%) }')
+            self.isbn.setToolTip(_('This ISBN number is valid'))
+        else:
+            self.isbn.setStyleSheet('QLineEdit { background-color: rgba(255,0,0,20%) }')
+            self.isbn.setToolTip(_('This ISBN number is invalid'))
+
     def show_format(self, item, *args):
         fmt = item.ext
         self.emit(SIGNAL('view_format(PyQt_PyObject)'), fmt)