diff --git a/lib/Test/LWP/Recorder.pm b/lib/Test/LWP/Recorder.pm
index 373dcea..95c1350 100644
--- a/lib/Test/LWP/Recorder.pm
+++ b/lib/Test/LWP/Recorder.pm
@@ -11,7 +11,6 @@ use base qw(LWP::UserAgent);
 use Digest::MD5 qw(md5_hex);
 use File::Slurp;
 use File::Spec;
-use List::Util qw(reduce);
 use HTTP::Status qw(:constants);
 use HTTP::Response;
 
@@ -29,22 +28,21 @@ sub new {
     return $self;
 }
 
-sub _filter_param {
-    my ( $self, $key, $value ) = @_;
-    my %filter = map { $_ => 1 } @{ $self->{_test_options}->{filter_params} };
-    return join q{=}, $key, $filter{$key} ? q{} : $value;
-}
-
 sub _filter_all_params {
     my $self         = shift;
     my $param_string = shift;
+
+    my %filter = map { $_ => 1 } @{ $self->{'_test_options'}->{'filter_params'} };
+
     ## no critic (BuiltinFunctions::ProhibitStringySplit)
     my %query = map { ( split q{=} )[ 0, 1 ] } split q{\&}, $param_string;
     ## use critic;
-    return %query
-        ? reduce { $a . $self->_filter_param( $b, $query{$b} ) }
-    sort keys %query
-        : q{};
+
+    return join("&",
+        map { "$_=$query{$_}" }
+        grep { !$filter{$_} }
+        sort keys %query
+    );
 }
 
 sub _get_cache_key {
diff --git a/t/filter_params.t b/t/filter_params.t
new file mode 100644
index 0000000..46e0f41
--- /dev/null
+++ b/t/filter_params.t
@@ -0,0 +1,48 @@
+use strict;
+use warnings;
+
+use Test::More tests => 7;
+
+use Test::LWP::Recorder;
+
+my $ua = Test::LWP::Recorder->new({
+    record => 1,
+    cache_dir => 't/LWPtmp',
+    filter_params => [ 'filterme' ],
+});
+
+
+# Same URL parameter strings should return the same result
+{
+    my @pairs = (
+        [ "foo=a&bar=b", "foo=a&bar=b" ],
+        [ "foo=a&bar=b", "bar=b&foo=a" ],
+        [ "foo=a&bar=b", "bar=b&foo=a&filterme=c" ],
+        [ "foo=a&bar=b&filterme=c", "bar=b&foo=a&filterme=d" ],
+    );
+
+    for my $pair (@pairs) {
+        my @results = map { $ua->_filter_all_params($_) } @$pair;
+        ok(
+            $results[0] eq $results[1],
+            sprintf("Got matching param string for '%s' and '%s'", @$pair)
+        ) or diag sprintf("Got '%s' for '%s',\nBut '%s' for '%s'", $results[0], $pair->[0], $results[1], $pair->[1]);
+    }
+}
+
+# Different URL parameter strings should return different result
+{
+    my @pairs = (
+        [ "bar=a", "bar=b" ],
+        [ "foo=a&bar=b", "foo=c&bar=b" ],
+        [ "foo=a&bar=b", "foo=a&bar=c" ],
+    );
+
+    for my $pair (@pairs) {
+        my @results = map { $ua->_filter_all_params($_) } @$pair;
+        ok(
+            $results[0] ne $results[1],
+            sprintf("Got mis-matching param string for '%s' and '%s'", @$pair)
+        ) or diag sprintf("Got '%s' for '%s' and '%s'!", $results[0], @$pair);
+    }
+}