diff --git a/lib/syntax_tree/node.rb b/lib/syntax_tree/node.rb
index 58335b00..b633a1c9 100644
--- a/lib/syntax_tree/node.rb
+++ b/lib/syntax_tree/node.rb
@@ -5173,7 +5173,7 @@ def self.call(parent)
 
       while (node = queue.shift)
         return true if [Assign, MAssign, OpAssign].include?(node.class)
-        queue += node.child_nodes
+        queue += node.child_nodes.compact
       end
 
       false
diff --git a/test/fixtures/if.rb b/test/fixtures/if.rb
index e5e88103..1963d301 100644
--- a/test/fixtures/if.rb
+++ b/test/fixtures/if.rb
@@ -59,3 +59,7 @@
     baz
   end
 )
+%
+if (x = x + 1).to_i
+  x
+end