diff --git a/lib/rubygems/resolver/api_set.rb b/lib/rubygems/resolver/api_set.rb
index 5475e626e6e7..dda357987829 100644
--- a/lib/rubygems/resolver/api_set.rb
+++ b/lib/rubygems/resolver/api_set.rb
@@ -34,6 +34,8 @@ def initialize dep_uri = 'https://rubygems.org/api/v1/dependencies'
 
     @data   = Hash.new { |h,k| h[k] = [] }
     @source = Gem::Source.new @uri
+
+    @to_fetch = []
   end
 
   ##
@@ -45,6 +47,10 @@ def find_all req
 
     return res unless @remote
 
+    if @to_fetch.include?(req.name)
+      prefetch_now
+    end
+
     versions(req.name).each do |ver|
       if req.dependency.match? req.name, ver[:number]
         res << Gem::Resolver::APISpecification.new(self, ver)
@@ -61,9 +67,13 @@ def find_all req
   def prefetch reqs
     return unless @remote
     names = reqs.map { |r| r.dependency.name }
-    needed = names - @data.keys
+    needed = names - @data.keys - @to_fetch
+
+    @to_fetch += needed
+  end
 
-    return if needed.empty?
+  def prefetch_now
+    needed, @to_fetch = @to_fetch, []
 
     uri = @dep_uri + "?gems=#{needed.sort.join ','}"
     str = Gem::RemoteFetcher.fetcher.fetch_path uri