diff --git a/Changes b/Changes
index 48cabf6b9..dbcf24c65 100644
--- a/Changes
+++ b/Changes
@@ -39,6 +39,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 ****  Fix loop error message to report line, bug513.  [Jeremy Bennett]
 
+****  Fix false UNUSED warning on file system calls.  [Holger Waechtler]
+
 
 * Verilator 3.833 2012/04/15
 
diff --git a/src/V3Undriven.cpp b/src/V3Undriven.cpp
index 142c92a58..97ea7863c 100644
--- a/src/V3Undriven.cpp
+++ b/src/V3Undriven.cpp
@@ -274,8 +274,9 @@ private:
     virtual void visit(AstVarRef* nodep, AstNUser*) {
 	// Any variable
 	UndrivenVarEntry* entryp = getEntryp (nodep->varp());
+	bool fdrv = nodep->lvalue() && nodep->varp()->attrFileDescr();  // FD's are also being read from
 	if (m_markBoth || nodep->lvalue()) entryp->drivenWhole();
-	if (m_markBoth || !nodep->lvalue()) entryp->usedWhole();
+	if (m_markBoth || !nodep->lvalue() || fdrv) entryp->usedWhole();
     }
 
     // Don't know what black boxed calls do, assume in+out
diff --git a/test_regress/t/t_lint_unused.pl b/test_regress/t/t_lint_unused.pl
new file mode 100755
index 000000000..1deb80a7b
--- /dev/null
+++ b/test_regress/t/t_lint_unused.pl
@@ -0,0 +1,22 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2008 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+$Self->{vlt} or $Self->skip("Verilator only test");
+
+compile (
+    v_flags2 => ["--lint-only --bbox-sys --bbox-unsup -Wall -Wno-DECLFILENAME"],
+    fails=>0,
+    verilator_make_gcc => 0,
+    make_top_shell => 0,
+    make_main => 0,
+    );
+
+ok(1);
+1;
+
diff --git a/test_regress/t/t_lint_unused.v b/test_regress/t/t_lint_unused.v
new file mode 100644
index 000000000..ad4a23147
--- /dev/null
+++ b/test_regress/t/t_lint_unused.v
@@ -0,0 +1,60 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2010 by Wilson Snyder.
+
+module t (/*AUTOARG*/
+   // Outputs
+   out,
+   // Inputs
+   in
+   );
+
+   input in;  // inputs don't get flagged as undriven
+   output out;  // outputs don't get flagged as unused
+
+   sub sub ();
+
+   // Check we don't warn about unused UDP signals
+   udp_mux2 udpsub (out, in, in, in);
+
+   // Check ignoreds mark as used
+   reg 	  sysused;
+   initial $bboxed(sysused);
+
+   // Check file IO.  The fopen is the "driver" all else a usage.
+   integer infile;
+   integer outfile;
+   initial begin
+      outfile = $fopen("obj_dir/t_lint_unused_bad/open.log", "w");
+      $fwrite(outfile, "1\n");
+      $fclose(outfile);
+      infile = $fopen("obj_dir/t_lint_unused_bad/open.log", "r");
+      if ($fgetc(infile) != "1") begin end
+   end
+
+   wire   _unused_ok;
+
+endmodule
+
+module sub;
+
+   wire pub /*verilator public*/;   // Ignore publics
+
+   localparam THREE = 3;
+
+endmodule
+
+primitive udp_mux2 (q, a, b, s);
+   output q;
+   input  a, b, s;
+   table
+      //a b  s  :  out
+      1   ?  0  :  1 ;
+      0   ?  0  :  0 ;
+      ?   1  1  :  1 ;
+      ?   0  1  :  0 ;
+      0   0  x  :  0 ;
+      1   1  x  :  1 ;
+   endtable
+endprimitive
diff --git a/test_regress/t/t_lint_unused_bad.v b/test_regress/t/t_lint_unused_bad.v
index 77443b028..9cdacf34b 100644
--- a/test_regress/t/t_lint_unused_bad.v
+++ b/test_regress/t/t_lint_unused_bad.v
@@ -3,27 +3,10 @@
 // This file ONLY is placed into the Public Domain, for any use,
 // without warranty, 2010 by Wilson Snyder.
 
-module t (/*AUTOARG*/
-   // Outputs
-   out,
-   // Inputs
-   in
-   );
-
-   input in;  // inputs don't get flagged as undriven
-   output out;  // outputs don't get flagged as unused
+module t (/*AUTOARG*/);
 
    sub sub ();
 
-   // Check we don't warn about unused UDP signals
-   udp_mux2 udpsub (out, in, in, in);
-
-   // Check ignoreds mark as used
-   reg 	  sysused;
-   initial $bboxed(sysused);
-
-   wire   _unused_ok;
-
 endmodule
 
 module sub;
@@ -53,17 +36,3 @@ module sub;
       if (0 && mixed[1:0] != 0) begin end
    end
 endmodule
-
-primitive udp_mux2 (q, a, b, s);
-   output q;
-   input  a, b, s;
-   table
-      //a b  s  :  out
-      1   ?  0  :  1 ;
-      0   ?  0  :  0 ;
-      ?   1  1  :  1 ;
-      ?   0  1  :  0 ;
-      0   0  x  :  0 ;
-      1   1  x  :  1 ;
-   endtable
-endprimitive