diff --git a/spacy/tests/regression/test_issue1539.py b/spacy/tests/regression/test_issue1539.py
new file mode 100644
index 000000000..6665f8087
--- /dev/null
+++ b/spacy/tests/regression/test_issue1539.py
@@ -0,0 +1,10 @@
+'''Ensure vectors.resize() doesn't try to modify dictionary during iteration.'''
+from __future__ import unicode_literals
+
+from ...vectors import Vectors
+
+
+def test_issue1539():
+    v = Vectors(shape=(10, 10), keys=[5,3,98,100])
+    v.resize((100,100))
+
diff --git a/spacy/vectors.pyx b/spacy/vectors.pyx
index 46997cccf..96a9d3435 100644
--- a/spacy/vectors.pyx
+++ b/spacy/vectors.pyx
@@ -151,7 +151,7 @@ cdef class Vectors:
         filled = {row for row in self.key2row.values()}
         self._unset = {row for row in range(shape[0]) if row not in filled}
         removed_items = []
-        for key, row in self.key2row.items():
+        for key, row in list(self.key2row.items()):
             if row >= shape[0]:
                 self.key2row.pop(key)
                 removed_items.append((key, row))