diff --git a/spacy/vectors.pyx b/spacy/vectors.pyx
index d6b59401e..86c8450ce 100644
--- a/spacy/vectors.pyx
+++ b/spacy/vectors.pyx
@@ -56,10 +56,11 @@ cdef class Vectors:
         self.i = 0
         self.key2row = {}
         self.keys = numpy.zeros((self.data.shape[0],), dtype='uint64')
-        for i, string in enumerate(self.strings):
-            if i >= self.data.shape[0]:
-                break
-            self.add(self.strings[string], vector=self.data[i])
+        if data is not None:
+            for i, string in enumerate(self.strings):
+                if i >= self.data.shape[0]:
+                    break
+                self.add(self.strings[string], vector=self.data[i])
 
     def __reduce__(self):
         return (Vectors, (self.strings, self.data))
@@ -124,25 +125,22 @@ cdef class Vectors:
         vector (numpy.ndarray / None): A vector to add for the key.
         row (int / None): The row-number of a vector to map the key to.
         """
-        if row is not None and vector is not None:
-            raise ValueError("Only one of 'row' and 'vector' may be set")
         if isinstance(key, basestring_):
             key = self.strings.add(key)
-        if key in self.key2row and vector is not None:
+        if key in self.key2row and row is None:
             row = self.key2row[key]
         elif key in self.key2row and row is not None:
             self.key2row[key] = row
-        elif key not in self.key2row:
-            if row is not None:
-                self.key2row[key] = row
-            else:
-                self.key2row[key] = self.i
-                row = self.i
-            if row >= self.keys.shape[0]:
-                self.keys.resize((row*2,))
-                self.data.resize((row*2, self.data.shape[1]))
-            self.keys[self.i] = key
+        elif row is None:
+            row = self.i
             self.i += 1
+        if row >= self.keys.shape[0]:
+            self.keys.resize((row*2,))
+            self.data.resize((row*2, self.data.shape[1]))
+            self.keys[self.i] = key
+
+        self.key2row[key] = row
+        self.keys[row] = key
         if vector is not None:
             self.data[row] = vector
         return row