diff --git a/bin/grep b/bin/grep
index 9b88a066..1f1864ed 100755
--- a/bin/grep
+++ b/bin/grep
@@ -146,7 +146,7 @@ sub parse_args {
 
 	my $no_re = $opt{F} || ( $Me =~ /\bfgrep\b/ );
 
-	if ( $opt{f} ) {           # -f patfile
+	if (defined $opt{'f'}) {           # -f patfile
 		die("$Me: $opt{f}: is a directory\n") if ( -d $opt{f} );
 		open PATFILE, '<', $opt{f} or die qq($Me: Can't open '$opt{f}': $!);