diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 34dbcda657..43298dc29c 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -388,7 +388,7 @@ def xsystem command, opts = nil
         result = nil
         Logging.postpone do |log|
           output = IO.popen(libpath_env, command, &:read)
-          result = ($?.success? and File.zero?(log.path))
+          result = ($?.success? and log_harmless?(log.path))
           output
         end
         result
@@ -410,6 +410,14 @@ def xpopen command, *mode, &block
     end
   end
 
+  # Returns true when the log file given by +path+ is empty or contains nothing
+  # but harmless warnings.
+  def log_harmless? path
+    File.readlines(path).all? do |line|
+      line =~ /warning: \w+\(\) is .+ misused/
+    end
+  end
+
   def log_src(src, heading="checked program was")
     src = src.split(/^/)
     fmt = "%#{src.size.to_s.size}d: %s"