diff --git a/core/src/main/java/org/jruby/RubyIO.java b/core/src/main/java/org/jruby/RubyIO.java
index 784692ac7e3..3dbec5f4cbc 100644
--- a/core/src/main/java/org/jruby/RubyIO.java
+++ b/core/src/main/java/org/jruby/RubyIO.java
@@ -3784,14 +3784,14 @@ public IRubyObject advise(ThreadContext context, IRubyObject[] argv) {
 
         POSIX posix = runtime.getNativePosix();
 
-        if (!(posix instanceof Linux)) {
-            return context.nil;
-        }
-
         RubyIO io = GetWriteIO();
 
         fptr = io.getOpenFileChecked();
 
+        if (!(posix instanceof Linux)) {
+            return context.nil;
+        }
+
         int fd = fptr.fd().realFileno;
 
         if (fd == -1) {