diff --git a/core/src/main/java/org/jruby/RubyIO.java b/core/src/main/java/org/jruby/RubyIO.java
index 115c2592799..144660fe82e 100644
--- a/core/src/main/java/org/jruby/RubyIO.java
+++ b/core/src/main/java/org/jruby/RubyIO.java
@@ -2619,9 +2619,9 @@ private IRubyObject ctl(ThreadContext context, IRubyObject cmd, IRubyObject arg)
             return runtime.newFixnum(close_on_exec_p(context).isTrue() ? FD_CLOEXEC : 0);
         } else if (realCmd == Fcntl.F_SETFL.intValue()) {
             if ((nArg & OpenFlags.O_NONBLOCK.intValue()) != 0) {
-                fptr.setBlocking(runtime, true);
-            } else {
                 fptr.setBlocking(runtime, false);
+            } else {
+                fptr.setBlocking(runtime, true);
             }
 
             if ((nArg & OpenFlags.O_CLOEXEC.intValue()) != 0) {